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Do I need to buy the '97+ crossover if I am going to upgrade to the '97+ water pump? Can I just keep my OE crossover and upgrade to the newer high volume water pump?

I did and you can but the coolant crossover was designed to work with the HO pump, so it would be ideal.

I do not recommend the water pump alone. You may experience problems with frost plugs and block heaters ejecting otherwise.

For this reason, I only offer the entire kit for online orders.

"Ejecting" . . . does that equal blowin' right out of the block?

You got it...

Water pump impellers are passive. If there is no path i.e open thermostat they just spin in the water they are not creating pressure. If this were the case when the thermostat's were closed (reguardless of whether there was 1 or 2) the coolant system would overpressurize.

Good explanation - now give us some idea of where the 18psi system pressure comes from.......and don't say engine heat.

How does the '97+ crossover prevent problems with frost plugs and the block heaters ejecting?

Water pump impellers are passive. If there is no path i.e open thermostat they just spin in the water they are not creating pressure. If this were the case when the thermostat's were closed (reguardless of whether there was 1 or 2) the coolant system would overpressurize.

Just reporting on what I've been told. The talk of this phenomenon started with GM in their initial testing of the pump. I had a hard time believing it myself, but someone on a forum reported repeat losses of his block heater after installing the pump only. I have only heard of a couple of cases of this, but would tend to believe it now.

I'd view the water pump as a centrifugal pump if sorts. A centrigugal pump is what I am using to supply pressure to the Dmax injection pump. A teeny little pump that can push to approx 24' of head with only 48 watts of current and a < 1" diameter wheel.

Now the A1 fuel controler, THAT'S passive...

Thanks Kennedy.

Good explanation - now give us some idea of where the 18psi system pressure comes from.......and don't say engine heat.
OK I won't say "engine heat" But I will say from the expansion of the water when heated.

Water pump impellers just create flow, flow with no resistance equal no pressure built up. BUT the impeller will only create a little pressure as compared to a piston and foot valve pump like the IP as an example.
Impeller has high flow with low pressure, piston type pumps creates high pressure with low flow.

Perhaps when the t-stat closes, there is a brief increase in pressure, especially given all the extra "flow" that the updated water pump provides. This short spike in pressure could be the cause for the freeze plugs being blown out. How the updated dual t-stat housing would prevent this I don't know.

Just speculating, as I know virtually nothing about diesels and or engine cooling (except what I've read here).

I'm not here to start arguments. This is my first diesel, so I'm learning as I go along(example a-1 fuel controler), which I keep in my sig. to warn others that might. I do however know pumps and fluid dynamics. Think about it if the t.stat or t.stat's are closed wouldn't that be exposing the H.O.'s output against the freeze plugs and heater, same as if the was only one t.stat. Regular t.stats are only capable of flowing about 35GPM high flows only about 55GPM. GM wanted to exchange the coolant faster and they didn't use high flow designs so they had to go with 2 t.stat's.

Of course the pressure comes from engine heat. That's how a PRESSURE cooker works liquid in a closed container add heat and what happens PRESSURE.

If I knew then what I know now I would not have spent so much money on the A-1 fuel controller. Just because changing the resistor has so little affect on quantity of fuel delivered. Bang for the buck it gets a 1 out of 10. When a wire fell out of the pin on his harness due to a bad crimp after only 2 month's I asked him to send me a new pin to crimp on, he wanted me to send him back the harness for 2+ weeks and $70 to repair. Rudest buisness person I've ever delt with. Since then I've sent all my friends to Heath and Kennedy.

Thanks everyone for your input. So it sounds like using a '97+ HO water pump with a '95 OE crossover would be fine. Honestly, I don't even need an HO water pump. However, my Burb is approaching the 140k mile mark with the original water pump. I was going to replace it this spring along with the accessory pulley as part of my on going preventative maintenance program. I thought I might as well just replace it with the HO water pump, if it would fit my old crossover. It sounds like it will, so I think I will probably go in that direction.

Water pump impellers just create flow, flow with no resistance equal no pressure built up. BUT the impeller will only create a little pressure as compared to a piston and foot valve pump like the IP as an example.
Impeller has high flow with low pressure, piston type pumps creates high pressure with low flow.
As does a turbocharger...

My recommendation stands. I do not suggest using the high capacity water pump w/o the appropriate crossover/t-stat combo...

Is the impeller-type pump in your pressure cooker operating as pressure builds, or only after some set-point in the pressure rise?

Something to consider in this flow vs pressure discussion, a LOT of design effort went into GM selecting the dual thermostat, if it were just enough to add a higher gpm pump then GM would have went that route only as the extra thermostat costs more money and GM or any industry NEVER adds anything to increase mfg cost for no good reason.

As temp goes up in any vessel so does pressure, that is a given, I don't know GMs thought on management of this exactly, but I suspect part of the dual thermostat design is to regulate flow more than it was concerned about pressure for a given range.

From my experiences on shipboard heat exchangers, I learned that you can actually at times have too much flow and a temperature regulator is required to regulate the flow. If temp of cooling medium (saltwater on ships, air in our trucks) were constant, and power level of heat producer were constant an orifice could be sized on cooler outlet, or specific sized pump for exact operating temp required and temp regulation would not be a problem.

Ships and trucks change location & speeds so power required/temp generated varies, and so does the temp of the cooling medium. In ships we sometimes had to set temp controllers for 50F seawater, move South to 80F water and we would have to adjust flow for that temp (same holds true in air say winter vs summer). Reason we had to adjust coolant flow is for a heat exchanger to work there has to be time for the heat to transfer to the medium carrying away the heat, too little flow the medium itself gets hot and can't carry away any heat, too fast a flow of coolant it does not remain in the cooler long enough to pick up any heat.

Back to the ship example going South to warmer water things got hot so naturally one would think we need more water, yes to a point, found out the hard way, more is not always better, with valves wide open things still got hot even with max available flow, throttle back for a little more flow than at 50 F and less flow than valve full open things stayed cool.

We can't run our trucks with little guys under the hood to watch temps and adjust a regulator valve for changing condtions, and an complex automatic regulation device would be cost prohibative, so the dual thermostat was least expensive best option GM could come up with.

When GM went with a larger GPM pump and dual thermostats to fix problems in early 6.5 I venture to speculate that the flow vs heat rejection calculation showed that while more flow was better in some instances, it was not desireable in all cases, requiring the dual thermostat for all possible operating scenarios. At high engine rpm with 130gpm on a single thermostat I suspect flow was too fast for proper heat xfer to the radiator so the 2nd thermostat works as a restrictor to slow flow. Also without the proper flow under right conditions temps & pressure elevate causing the problem, probably some cavitation in the cooling system with too much flow as well.

As for the larger pump making more pressure, it is quite possible that it does, just depends on shape of the pump housing internally, only way to know for sure is to put a gauge on it and see what system pressure is, both ways large and small pump. I have seen tiny pumps that make a lot of pressure but no flow, and big pumps that make flow and lower pressure, and pumps that do both increase pressure (to a point) and also have more gpm.

IIRC physics lesson generally for volume to go up pressure comes down and vice versa on exact same sized pumps/nozzle etc.; but if you change the physical size and you can alter the pressure vs gpm relation, add heat to the mix one cooled vs one hotter can also change things up, which is why I say only way to know for sure is to gauge the system.

Bottom line is I would not myself go single thermostat and H/O water pump only, I was reminded earlier that either here or on The Page a member after doing HO pump only blew out the block heater plug a couple of times. Was it more pressure from a higher gpm pump or higher pressure from an incorrectly hotter flowing cooling system with more heat generated pressure; I don't know and can only speculate.

Thanks Turbine Doc, that explanation sounds very reasonable to me. I could see how just increasing flow rate, could actually cause the engine to run hotter.

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However, I also agree with others on this forum who argue that a water pump on an automobile is designed for flow rate rather than pressure. According to Bernouli’s principles of fluid dynamics, with increased flow rate there is a drop in pressure. Therefore I am not convinced that just upgrading the HO pump without upgrading the crossover would actually increase pressure and therefore cause damage to other components.
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Since I do virtually no towing with my Burb, perhaps I would be better off just installing a replacement OE water pump.

Thanks Turbine Doc, that explanation sounds very reasonable to me. I could see how just increasing flow rate, could actually cause the engine to run hotter.

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However, I also agree with others on this forum who argue that a water pump on an automobile is designed for flow rate rather than pressure. According to Bernouli’s principles of fluid dynamics, with increased flow rate there is a drop in pressure. Therefore I am not convinced that just upgrading the HO pump without upgrading the crossover would actually increase pressure and therefore cause damage to other components.
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Since I do virtually no towing with my Burb, perhaps I would be better off just installing a replacement OE water pump.

I hear the "I don't tow" reasoning frequently, typically followed by a call looking for heads later on down the road.

If a water pump cannot make psi, then how does my centrifugal lift pump do it?

Much of the psi issue revolves aroung the bypass blocker on the thermostat I believe...

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Since I do virtually no towing with my Burb, perhaps I would be better off just installing a replacement OE water pump.
This is one of the must do mods for longevity IMO, GM acknowledged their shortfall in original design by modding all 6.5 equipped vehicles, even the "lowly underpowered :D L56 light duty such as mine " came with it.

Bernoulli's law was based on a head of pressure forcing a volume of water thru a hole into open air (Q = Area x sq rt of 2gh).
Pipeline measurement uses that formula (Q = sq rt of Pressure x Diff press) for calculating flow throughout the industry, petrochemical and other wise.
Still, a pressure head into an open-ended system.

And, the pressure drop is measured in inches of water, not psi - 27"H2O = 1psi - where head pressures of 650psi and volumetric flow rates of 1.5 million cuft can give differential pressures of 150"H2O to 270"H2O, or 10psi.
Rather insignificant pressure drop when compared to 650psi head.

Fortunately, that cannot be applied here - the head pressure in this system is generated by a pump, of which pump intake is from the other side of the restriction.
That restriction being the engine block and heads, not a round orifice into an open-ended volume.

Surf back up a few posts to the first sentence in Bowtie's second opening gambit for the truth of the matter - an impeller-type pump (and others) flowing in a circuit with no restriction generates no pressure, only flow.

Further, if any volumetric output of the pump is less than the flow thruput of the circuit, any little pressure will be developed due only to the friction of the circuit containment walls - plumbing, and such.

The diameter of the impeller, the span, width and number of vanes in the impeller determine the pumping volume.
Those factors and the impeller circumferential and vane-to-wall clearances in the pump determine the amount of head pressure which will be developed against the restriction - the engine coolant passages, in this case.
The t-stat(s) have a small 'bleed' orifice, which eliminates initial system air bubbles and equalizes system pressure on both sides of the closed t-stat(s).

When max system design-pressure is reached, the coolant bypasses around the impeller clearances to the impeller intake, preventing further pressure increase.

The pump will develop system pressure within 30 seconds of cold engine starting, providing no air is in the system, say, from empty coolant reservoir.

The small pressure increase over system pressure due to coolant expansion from thermal input is easily handled by the Coolant Overflow Reservoir, which does have a finite volume.
A volume easily exceeded when coolant temps are allowed to reach vaporization temperature (steam), and one reason for which the coolant system is pump-pressurized - temperature at which water boils increases as pressure increases.
Anti-freeze additive also raises boiling point, as well as prevents oxidation\corrosion, insuring excellent thermal transference.

The HO pump and dual t-stat crossover manifold increased overall system flow from max85gpm to 130gpm - 75% increase thru the block and heads, 15% thru the radiator.

Having rebuilt many engines bare-block up, I have seen original freeze plugs that externally appear functional, but when knocked out show to be rusted nearly thru, so I am skeptical of the 'freeze plugs popped-out after upgrading to the HO pump' scenario.

And having purchased new factory items which were ruined in production, I am aware that factory testing of the improved coolant system, with resultant popped-out freeze plugs and block heaters, may only have 'illuminated' some ongoing productivity problems.

And '75% improved flow thru block and heads' could also mean that the original flow was 75% deficient.

But, even with the improved flow capabilities, the larger fan and lower thermal cut-in fan clutch are also required to control engine temps under sustained loading, proven time and again.

If the vehicle has the bypass block-off single t-stat, the HO waterpump can 'illuminate' any potential system problems, in short order.

If the vehicle has the '96 single t-stat constant bypass system, the upgrade requires only the pump and\or manifold - the factory installed hoses fit either system.

The upgraded system is an inter-designed package, with intrinsic caveats not to be ignored.

That's my story, and I'm stickin' to it...............

[QUOTE=Kennedy]I hear the "I don't tow" reasoning frequently, typically followed by a call looking for heads later on down the road.

QUOTE]

What are you selling, the cooling mods or the fear of not having them. My truck made it 310,000 miles without cooling mods. My dad's '96 is pushing 250,000 without and we pull trailers in the texas heat.

I have my own theories on why these trucks crack the heads and blow the head gasket and I'm of the opinion constant vigiliance and proactive maintence of the system coupled with a good understanding of the system can head most of these problems off before the heads are blown.

The stock system could be said to be 75% defficient in flow but then add to that the heat from the tranny and the a/c and now we're raising the ECT guage sitting still. I'd go for the flow increase/fan clutch just for that.

i have been running the '97-up pump with a single tstat housing since early summer 2004 when my original pump began leaking. i also do not have a tstat in the housing. i believe that my heat, although slow to heat up, still works because of the larger bypass of the single crossover. because of the water jacket design in the heads the pre-cups get plenty hot and have not adversely affected my efficiency or idle. the only thing i want to try next is a manual shut off for the bypass to be used in the summer to force more flow directly through the radiator. if you call me crazy i just might agree with you but it works and i have not overpressureized anything or had any ill effects. okay okay let me have it tell me why i'm wrong and looking at impending doom.

[QUOTE=Kennedy]I hear the "I don't tow" reasoning frequently, typically followed by a call looking for heads later on down the road.

QUOTE]

What are you selling, the cooling mods or the fear of not having them. My truck made it 310,000 miles without cooling mods. My dad's '96 is pushing 250,000 without and we pull trailers in the texas heat.

I have my own theories on why these trucks crack the heads and blow the head gasket and I'm of the opinion constant vigiliance and proactive maintence of the system coupled with a good understanding of the system can head most of these problems off before the heads are blown.

The stock system could be said to be 75% defficient in flow but then add to that the heat from the tranny and the a/c and now we're raising the ECT guage sitting still. I'd go for the flow increase/fan clutch just for that.

You do what you want, but on my end, I'd rather set a guy up so that the only followup call made is to tell me how good it works. As Turbine Doc stated earlier, GM wouldn't have spent money where they did not need to. Heck they even orphaned the 96 single stat crossover and outlet after 1/2 year...

Lupey

The damage you may be causing by not running a thermostat probably won't show up for quite some time. I can't believe people still believe that theory.

You'll immediately agree if you try and tow something substancial.

billy-
please explain

What JK is "selling" is pay now or pay later advise I won't say much more than this; you have your opinion, & others have theirs. Everyone has made their opinion known, it's now up to individual readers to weigh all info and decide which is best for their truck.

It's not worth a never ending diatribe debating the point if single thermostat with a HO pump is sufficient, GM has spent serious research money on this problem I'll defer to their Engineering science, I wish they would have put same effort on the FSD/PMD problem.

QM IMO up to now you have been rolling the dice and winning, best of luck to you for continued operation, maybe this works for you. TX and MS heat nearly the same, when I tow 18K loads I'm very glad I have the dual set up, additional trans cooler, and the modded fan clutch, for me it's cheap insurance on an expensive engine, and saves from having to walk home or be towed.


[QUOTE=Kennedy]I hear the "I don't tow" reasoning frequently, typically followed by a call looking for heads later on down the road.

QUOTE]

What are you selling, the cooling mods or the fear of not having them. My truck made it 310,000 miles without cooling mods. My dad's '96 is pushing 250,000 without and we pull trailers in the texas heat.

I have my own theories on why these trucks crack the heads and blow the head gasket and I'm of the opinion constant vigiliance and proactive maintence of the system coupled with a good understanding of the system can head most of these problems off before the heads are blown.

The stock system could be said to be 75% defficient in flow but then add to that the heat from the tranny and the a/c and now we're raising the ECT guage sitting still. I'd go for the flow increase/fan clutch just for that.

Gm has them, I am sure they are capable and have looked at every aspect of the hcooling system.
One thing that i want to add. Has anyone looked at the cooling on the new VW's, the ones with that funky v6 and v8 engines, real narrow, almost an inline? i aks because the engineers there, just like turbinedoc pointed out, looked at cooling flow compared to heat transfer. but they SLOWED down the flow, substantially so. So much in fact the heater would no longer work because the water went thru it to slow. That is the reason they have an elcetric pump in the heater circuit.
I cannot see the harm nor benefit to running a HO pump with stock t-stat setup like that. The pump will cavitate more, obviously. But make enough pressure to blow out freeze plugs, not likely. I have pressured my own 6.2 cooling system up to 30psi before trying to find a stubborn leak, and the freeze plugs are still in it. The design of the waterpump will not let it make any substantial pressure, just take on apart and look at it, you will see why real quick. The comparison to the centrifugal lift pump is like comparing apples to oranges. The blades in the pump are flungout against the outer liner, and build pressure, much like the transfer pump in the injection pump, except we have small springs to keep them in contact with the liner.
The blades of a water pump NEVER make contact with the housing (at least they shouldn't).
IMO, I say run it, then later if you have money upgrade the t-stats, you will have already done the w/p so you wil be ahead there.
One more note, ever seen those underdrive pulleys for the gassers, slows down everything. Slows the acc down enough to a/c and p/s will not work at idle. We also have run them in dirt track cars, never an overheating problem. Anyone ever think of slowing down the flow on the 6.2/6.5 and seeing what happens?
Brian.

It's not that I disagree with anyone here as to end results. I am sure I'll get the dual t crossover sooner than later but with my radiator on it's way out I know what will come first.

As for my luck, I never had any 'till my father gave me his. What I have is an intuitive nature. I can usually find the weak spot in anything without trying. Things may appear to spontaniously break when I touch them. I've tought myself to fix it, whatever it is, even if it's theoretical.

Gm has them, I am sure they are capable and have looked at every aspect of the hcooling system.But those same people that ya are so quick to trust then put your PMD back on the pump where THEY say it belongs.

IMO, I say run it, then later if you have money upgrade the t-stats, you will have already done the w/p so you wil be ahead there.YEAPPER Cause some of us don't have the money to buy it all at once and I believe that the newer WP is better than using the older one. Too bad JK doesn't see the need to sell parts without selling the whole kit. Guess I'll have to keep my dealer parts guy working for my parts( BTW I can by everything @ same $$ as the kit and buy it by the piece) with no shipping. I will however continue to look into the modified fan clutch from JK. Not sure if I want the fan engaged all the time that It seems that the clutch will do that but thats another topic

OH BTW Howdya from Turkey

Turkey, as in the middle east?

Turkey, as in the middle east?
YEAP That be the one.

Be well, my friend.

Some people just dont get it.....

bowtie--i have the 170deg. fan clutch from heath and it helps. the fan does not engage all of the time the 170 does not correspond to the coolant temp rather the under hood temp at the clutch.

aslo-- i still want to know what damage i'm doing not running a tstat.

Would you hear/notice the fan engaging? I think it would make quite some noise, but I've never noticed mine yet. It is large and even drawing quite some air at idle, unengaged, so it must create some kind of storm when running at full power.

Does the fan clutch engage 'immediately' once the temperature it's set to is reached, or does it engage 'softly', i. e. a little bit more for each degree temps come closer to its set point, until it's fully engaged?

Under what circumstances does overheating occur? Does it take towing great loads through the heat, or can it even happen at normal driving?

Some people just dont get it.....What people and what don;t they get????
Explain this comment please

bowtie--i have the 170deg. fan clutch from heath and it helps. the fan does not engage all of the time the 170 does not correspond to the coolant temp rather the under hood temp at the clutch.

aslo-- i still want to know what damage i'm doing not running a tstat. guess I didn't know Heath had these. I thought only JK did. I will be looking it to it as I upgrade my truck in the future.

Regarding the dual t-stat. I was helping my friend replace his this weekend on his 98 6.5. He bought it new and never had to replace them before. Funny thing is one is a 180 degree and the other is a 195. Say so in small writing on the stat.

Isn't that the factory combination?

I guess it is.. Just seem strange to have two different stats.. Does the kits you buy have these two stats as well?

I can't say. I read that was the stock combo on the gm-diesel forum. It makes sense to me. The first opens at 180* opening flow to whatever one Tstat flows (175 cfm?) effectivly slowing down the passage through the radiator allowing the truck to further heat till the second opens at 195*.

Lupey

My comment was May. It doesn't necessarily mean You are.

By not operating at Full(or operating temperature), for extended periods of time(read: thousands of miles), Things don't expand properly.

Piston skirts and cylinder walls suffer.

Longevity is reduced.

At least that is what I believe. Take it for what it's worth.

Everyone here's got an opinion. That's mine.

Anybody who has towed any decent amount of weight for a decent amount of miles has thermostats. Be it 180 or 195. Just ask them.

Don't believe me? No need for me to explain. Hook up to a big trailer and go. You won't get 5 miles.

Lupey
Don't believe me? No need for me to explain. Hook up to a big trailer and go. You won't get 5 miles.AH But there was a need for you to explain and you did just that. The explaination was asked for by someone who didn't understand what you have now taken the time to explain.
THANKS
:)

Olee,
In reply to your questions about the fan, no it is not enguaged all of the time, yes you can tell when the fan comes in and it does sound like a worlwind, it seems to come on rathery quickly and when the temp falls it goes out quickly. When it comes in the temp drops quickly, even on a long up hill pull.

To all else,
I am having problem with my cooling. I bought the fan clutch from Heath. But my temp still gets very high before the fan comes in. On a long pull in the summer my temp will rise to about 220 then the fan comes in strong and the temp falls to 195 and the fan falls out. That is what my temp guage says. What is the first step to finding the problem; Clutch problem, guage problem, radiator problem? Still have stock pump on 1995 suburban, and stock fan blades. Pull #15,000 total weight.

Boise Biker welcome to the site,

You mostly stock except fan clutch, is 15K what you are hauling or combined weight, pretty heavy for stock rig, in stock dress with that weight, you will run hot. You need to start doing some mods, visit FAQs for ideas, update your sig so we know what flavor of truck we are talking about as outfitted by GM via RPO codes in glovebox, also read welcome announcement.

Thanks for having me.
It isn't very stock, but here I go. 4.10 gears, 2500, 4X4, 4L80E with shift module from Heath Diesel, plus signature stuff. #15,000 combined weight, that is two trailers in tandem. 211,000 miles and runs great. Also a Heath Diesel FSD relocation Kit, and a AFE air fliter with the snorkel removed. I think that is it. I have the most problems when the engine is in high boost situations, boost is set to 11psi max. Of course this is on big hills. No problem on level ground at any speed. I think that the radiator is the biggest one I can get, but I can't tell how many cores is has, 2, 3, or 4 core.
It pulls pretty good but I think there is more to be had. My question is why doesn't the fan clutch come on sooner like it is supposed to. When I hit a hill the temp rises to 220 before the fan comes in. I replaced the thermostate with a OEM.
I am a Mechanical Engineer and design cooling systems for locomotives so this is nothing new to me. I think I will eventually figure it out but thought I would ask if maybe others have had similar problems and how they fixed them. I appreciate any help or advise I can get.

The HO water pump/crossover is out there for ~$300. Said to improve flow ~75%
Don't forget the tranny's disapating it's heat in the radiator and can help raise the temps.

Also I am told that the front of the radiator gets really clogged with junk after that many miles. I think HoweE has pictures on hie website of his and how to clean it up. That and the cooling upgrade would have to help this some I'm thinking.

Do the radiators get clogged on the inside very easy? Will rodding the core clear up any problems? Don't know previous history on the vehicle.

Thanks,

No, when these radiators go they can be disassembled and cored but it's the front between the cores that all the crap piles up.

Can't hurt having a good radiator shop to look and clean the inside of your radiator. May not need anything but hard to tell till you look. Also removal allow you to remove the build up of bugs and other road junk. That will 'fer sure' be a big help.

Whew! Someone dug this thread up. Update! I put my 180deg tstat in, where it should be.

A Very Wise choice Lupey...

At the risk of "spitting into the wind," I'll make a comment here.

How do you get flow without a pressure differential? If water pump impellers generate flow, but not pressure, what makes the coolant move?

A very similar system is used in water well pumps. How does one of these push water into a pressure tank that has a pressure switch set to turn the pump off at, say, 60 psi? Believe me, the water doesn't want to go in there.

There are basically two types of pumps: positive displacement and dynamic.

A positive displacement pump (piston pump, gear pump, vane pump, etc.) moves a specific volume of fluid during its operating cycle, no matter what the back pressure is. With this type of pump, if you shut off the outlet flow but keep the pump running, something will break because pressure will increase uncontrollably. These pumps are very useful when you need to know that a certain flowrate is being achieved but you better have a good regulator with a big enough bypass to keep things from breaking.

A dynamic pump, on the other hand, has a varying flow capability based on back pressure. Guess where the back pressure comes from. The pump pushing the fluid into the downstream plumbing. The flow rate for this type of pump is maximum when the back pressure approaches zero. The flowrate approaches zero as the back pressure increases. Flowrate with a dynamic pump can reach zero if the back pressure is high enough to stall the flow and cause recirculation to take place in the impeller.

If you plumb a pressure gage downstream of an impeller-type pump and upstream of a valve, you can watch the pressure increase as you close the valve...try it sometime. That impeller is doing work on the fluid which raises its static pressure.

The back pressure at which an impeller will stall (cavitate) is based on its size and speed of operation. A larger impeller will stall at a higher back pressure than a smaller impeller. Think of it as having more leverage over the fluid to make it flow. If the flow rate is externally set (i.e. with a valve, or existing downstream plumbing) and a larger impeller is installed in the system, the operating back pressure of the pump will be higher.

This is what we're talking about here with the high volume pump vs. the stock pre 97 pump. The claims of plugs and heaters popping out originated with GM, not Kennedy. The system pressure will be higher if you only change the pump...a bigger impeller is trying to push more flow through a system with a set restriction. The flow rate will be higher (because of the increased pressure) but not in proportion to the change in impeller size.

I do not recommend the High Volume pump without the new crossover. Some have been successful running this way, but the risk of engine damage from loss of coolant is more than I would want to endure.

The idea that increased flow is bad for cooling is a misunderstanding of observed phenomena. Increasing flow rate increases the convective heat transfer coefficient and increases the rate of heat transfer. The issues with running hot because of running no thermostat are caused by bypassing the radiator. The flow restriction of the radiator makes it harder for the coolant to flow through than to bypass and go directly back into the block. The thermostat causes the fluid temperature to increase to the point that system pressure is high enough to force a significant percentage of the coolant through the radiator.

Not Too much spitting in the wind here RJ. The only small point I'd like to make is that the water pump, new style or old style will only generate XX pound of pressure. The plugs and heaters are designed to hold more than the XX pounds that the just water pump can produce with it's impeller style pump. A impeller style pump will continue to turn even after it has reached its max pressure based on what ever the back pressure is. Example: Cooling system designed to with stand 20 PSI. Most of this pressure comes from the heating of the water in the closed system by the motor and not from the water pump. The water pump number one job is to move the water(flow) but when the flow has stopped due to back pressure of whatever cause, the water pump keeps on turning. So the plugs and heater coming out, IMHO, is more from the fact that they weren't installed corrrectly or needed replacement or new seals.

Thats just my view of this small world and Oh course I ain't nobody :eek:

True enough, bowtie - an impeller-type pump is not a positive-displacement pump, in any sense of the word, and does, in fact, function well in limited pressure systems by allowing flow to 'bypass' around the impeller blades.

Concept of flow being too-fast to remove heat comes from gasser engines without constant-recirculation bypass - removing t-stat allows water to flow thru radiator too quickly for low-density air-over to remove heat from hi-density coolant.

Replace t-stat for normal operation - increase radiator surface area to improve heat exchange, where required.

Waterpump flows hi-volume at hi-rpm, where hi-power heat can be managed, usually with one t-stat porting to radiator.

Gassers do not produce much heat at low rpm, where wp produces low flow - one t-stat is adequate.

Diesels can produce great power at low rpm, with great heat - low rpm wp output is low, requires less restriction to allow more flow to radiator.

Dual t-stat allows more flow to radiator at low rpm hi-power event, as in towing 15000lb backhoe in 4rth-over at 1700 - 2200rpm.

If main vehicle use is driving granny to wally-world for a quart of Geritol, dual t-stat improvement will not be evident.

Pull granny's double-wide two-story across the rockies as she relocates to kalifornia - you'll notice the improvement, rather quickly, ahbp.

Bravo, Bravo
Well Said Gmctd, Well Said

gmctd, not pulling granny's double-wide but I am pulling my truck up some pretty steep hills (~50*) in 4-LO, 1st gear at about 1500-2000rpm. Direct sunlight temps probably reach close to 130deg in the summer. Had to pull off the trail a few times to let it cool down. I'm assuming the t-stat upgrade would help in this situation...right?

The upgrade consists of the dual t-stat manifold, HD hi-output waterpump, multi-blade fan, revised clutch.
The 130gpm package improves coolant flow thru the block by ~75%, thru the radiator by ~15%, a tremendous improvement over the '95 85gpm system.

Also required is new downpipe, DMax 21" fan blade, recalibrated 190deg fan clutch.

External trans and engine oil coolers do remove tremendous heat-load from engine coolant, with aux electric fan on each cooler required for that really slow work.

In your off-road situation, the '97 upgrade will help, but with little to no forward airflow at that slow pace, you'll need the low cut-in fan clutch, larger DMax fan, and aux fans on the external oil coolers.

The '90's series trucks are also efficient road vacuums, packing the area between the radiator, ac condensor, and oil coolers with an amazing variety of road-trash.
Off-roading would seem to offer much more variety in that area, more often.

Removing radiator to clean those inter-core areas can be an annual requirement, moreso if off-roading is frequent.

So - yes, it is a big improvement over the '95 system, but will need further upgrade, in your case, because you will not have the tremendous forward air flow available at on-road and hi-way speeds.

Larger fan, and aux electric fans will be part of your solution.

BTW - a charge-air cooler would help, but would require forced air-over to be functional at crawl speed.

Yeap GMCTD you pretty much covered that too.
The only thing I have questioned in the past and haven't been able to get answered is the revised engaged temp fan clutch. Does it stay engaged all the time at that temp??
or just when engine working. Also what about the 97 and newer non Dmax fan?

About the heavy duty fan clutch, mine is suposed to come in at 180°F but when I hit a big hill the temp guage reads 220 before the fan comes in. Then the temp falls of quickly. How come it waits to come in, how can I get it to come in sooner, is it possible my temp guage is off? So many questions.

Thanks,

Don't know where yours came from BUT if it's a Kennedy I bet it coming on close to right. As I understand them and please JK tell me if I' wrong, it starts to lock up at 180 and comes on fully by 195, I think. As to your gauge, I wouldn't call them really accute type. You could put aftermarker under hood to check against.

There is only one clutch that comes in at 180°f and it is made for me by Borg Warner. Aside from the special calibration, it is an OE unit. There are others that claim to have different temps, but in fact are simply OEM units.

One thing you need to remember here is that the cut in temp, while related to coolant temp is NOT entirely related to coolant temp. It is air temp induced, and air flow cahracteristics as well as radiator condition and ambient temps play a big part.


About the heavy duty fan clutch, mine is suposed to come in at 180°F but when I hit a big hill the temp guage reads 220 before the fan comes in. Then the temp falls of quickly. How come it waits to come in, how can I get it to come in sooner, is it possible my temp guage is off? So many questions.

Thanks,

I realize that it is the air temp that hits the fan, and by the way it is a Heath Diesel Severe-Duty Fan Clutch. My bad it starts in at 185° and is fully enguaged at 190° according to Heath. But my guage tells me differently. I have yet to put a different guage in the coolant, future plans. I cleaned out the space between the cores last summer and it was durty, but I still had the same problem, fan comes it too late. Is it possible that the core is durty inside and therefore not transfering the heat to the air? Has anyone had there core rodded and was it gunked up?

OEM spec is 195°f Mine is 180°f The Hayden unit is the same as you'd get from a GM dealer.

Heyden makes a lot of claims about fan clutches...none verified. I've done some investigation of fan clutches and find their claims to be dubious. I run Kennedy's clutch. It works as advertised.

BUT RJ what fan do you run. I understand that JK's clutch will fit both the steel 97 and up fan and the Dmax plastic one. Is thie also true?

Yes.

I run the 20" 9-blade steel fan rather than the 21" Duramax plastic fan. This decision was based on comments from the Borg-Warner engineer who designed the clutch.

Both fans will bolt on.

I have JK 180° fan clutch and the 20" steel fan.

I tried 180° thermostats and I didn't have good results with them.

With the 180° stats the fan would engage and cool the air flowing throught the radiator off and the fan would disengage while the engine temp was still rising. I switched to NAPA 190° stats and that fixed that issue.:cool: If I ever get an intercooler I plan to try my 180° stats again.

Remember, boisebiker - the fan clutch engages at the temperature of the air flow in the center of the aluminum heat exchanger known as the radiator.

If your 180deg coolant does get thru your 180deg t-stat, and into the radiator hot tank, the temperature will start dropping as it enters the multiple cooling tubes.

If coolant temperature is still 180deg when it passes the middle section of the radiator, behind which section the fan clutch resides, you have serious other problems.

The fan clutch engages at temperatures above 180 deg - if the coolant temperature indicates 220deg before engagement, then the radiator, and fan, is doing it's job, when the t-stat(s) begin to open

A job directly related to ambient temperatures and volume of airflow thru the radiator.

On a very hot day, a\c burning, engine idling, you may notice coolant temperature is much closer to calibrated clutch engagement temperature

BTW - the '94-'95 single t-stat and manifold was a dual-valve bypass type, recirculating coolant thru the block by blocking radiator flow when closed, then blocking the bypass as the t-stat opened to the radiator.

This provided stabilized coolant temperature in normal driving - no wild hot-cool hot-cool swings.

Problem occured when loaded, or towing - coolant temp climbed, would not drop until vehicle was slowed to crawl, downshifted.
Some temps required vehicle to be stopped, idling.

The block radiator or block bypass system was discontinued in the upgrade, to a constant-bypass system, such that coolant always recirculates thru the engine, whether t-stats are closed or open.

Food fer thought, dudes.....

I have JK 180° fan clutch and the 20" steel fan.

I tried 180° thermostats and I didn't have good results with them.

With the 180° stats the fan would engage and cool the air flowing throught the radiator off and the fan would disengage while the engine temp was still rising. I switched to NAPA 190° stats and that fixed that issue.:cool: If I ever get an intercooler I plan to try my 180° stats again.
one 180* and one 190* might give better results but I havn't personally tried it. That's the factory set up.

So what do you all think of this, I've never seen or heard my fan stop spinning. It spins at startup and keeps on going. Is this an upgrade that the previous owner possibly did, or is this a problem? I believe some upgrades were perfomed for the fact that when I went to go and remove the snorkle, it was missing!!!

To the best of my knowledge the fans always spin, but they dont spin at the same speed as the pulley they are slowed by drag resistance of the air. then when the oil in the clutch heats to a certain tempurature it locks up forcing the fan to run at the speed of the pulley pulling more air through the radiator until the clutch cools down and releases the fan again.

I don't think I've ever seen it change speeds. So with that, what would it harm for your fan to be always running at full speed with the engine (clutch locked at all times)?

That would be very hard on the waterpump bearing at sustained hiway speeds - may be helpful when crawling, tho

The fan does spin constantly, just not fully engaged until coolant temp requires it.

Again, thermal cut-in is the temperature of air-flow thru the radiator, which is an average of the hot-side, cooler middle, and cool-side swirling across the fan assembly.

Normal under-hood heat is ~150deg, when vehicle is moving forward at on-road speeds, with normal forward air-flow.

Which should just about reflect avg air temp thru the radiator at on-road speeds.

Most fan clutches I pull off are covered in oily grime. I wonder how effective the thermal clutch can be when it's that dirty.

The dirty cooling fins will affect the longevity of the clutch and the engaged speed, but not the air temperature at which it engages. The fan will never turn at 100% pump speed, by the way. The engagement temperature is controlled by the bimetallic spring and the clocking of the internal valve mechanism.

If covered in oil then it's leaking most likely and that is a bad fan clutch.

No, It's road grime most likely.

Has anyone looked at the system that Heath Diesel has on thier site now as a cooling upgrade?

No. but thanks fer the heads-up..........

QM Most the fan clutches I've seen working at the parts counter and changed while bending wrenches that have oil soaked dirt are leaking. Most road grime wouldn't cause the oily film. The fan clutch seed oil out and the dust and dirt in the air sticks to it. May take awhile before the clutch goes out from loss of oil inside too.

Yes, in fact, I talked with him about it in depth about two weeks before they put it on the site. He's tested each head on their test 6.5 with 12 temp. gauges (in each head, I think) by drilling/tapping with a temp probe. They found that by the time the water is to the rear of the heads (toward the firewall), the temps were upward of 280 degrees F. The normal gauge, however, in the front of the head reads normal, as we see on the dash gauge.

I'll be making a purchase of one shortly.

I'd suggest to call and talk to Bill about this because he can give much better info, since he's the one that designed the system. I'm not a paid advertiser or anything, but just use many of his products on my 6.5. He's one heck of a good guy to deal with and I trust what he says.

SnowDrift

Hey SnowDrift thanks for the infomation. Can you tell us more

Just that it seems that this is the reason there are so many 6.5s with cracked heads on those rear cylinders - that much heat makes steam, which doesn't transmit heat out of the head. It's suppose to be a bolt on installation using a port in the rear of the heads (by the firewall). I asked about the limited space back there and I think he told me that if you can get to the oil pressure switch, then you can get to this port. Stainless steel reservoir and blue silicone hoses (I think the hoses are silicone).

I guess I'm going to justify this purchase in that it will be insurance. $250-300 for the kit vs. replacing the heads at $500 each. I think it's a good idea and look forward to getting my hands on this kit.

SnowDrift

Someone else had made their own a got poo poo'ed for it. It seems like it had enough merit for Heath to embrace.

Or - it was the 6 temperature probes per head that proved the front-to-rear equalization............

Snowdrift will you keep us posted on the new system after you install it?

I'd like to see pictures and make my own of course.