What are the pros and cons of running 180 degree thermostats vs. 195 degree?

Would this be a good option for keeping coolant temps down while towing? Will there be a downside when not towing?

Thanks,
Dave

I have a 180 Robert Shaw sitting on the shelf in my garage. I had to swap in a stock 195 to set the timing last fall and never swapped the 180 back in again.

So one disadvantage of the 180 is that it's hard to reach the operating temp required by the time setting functions.

180 pro's

Lower under hood temp - benefits the FSD/PMD if under the hood and all the other underhood plastics/rubber and various components.

Cons

Lower engine temperature. Diesels like a warmer block; it makes the engine more effiecient to run at 195 as long as intake air charge is the same (cool as when engine is at 180).

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Thermostats temp should not cause or solve an overheating problem (if they are working correctly). But may reduce temp swings that will engage the fan. I run (2) 180F thermostats and my truck usually runs about the 180-185 (dang GM odd ball tick mark on gauge is hard to remember exact number) and rarely moves normal driving. When towing it fluctuates according to load. It can go up ~10-20 degrees also depends on if A/C is on. That shifts the pivotal operating temp a little higher.

Now if they were 195F and you add 20F the fan might start to engage and take more power from the crankshaft (guesstimate 10-20 HP). I think the AC compressor robs about 6 hp and I can feel that engage so I don't want up to 3 times that taken away when I am working the engine hard.

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I don't know but I feel like there is a reasonably significant difference in a 20F swing across 212F. I know ECT is only one measure other areas are hotter and cooler but something still bothers me about too much moisture steaming as I think steam can super heat differently than water. I have no science to back that up as to how or where this moisture can act but something I think is different there.

OK I know it can get hot up north too but for how long. Down here depending on where you are at it doesn't cool off until 10PM and seems like never sometimes.

Once when I had a stuck open thermostat did I have a problem getting over 160F ECT within the time limit and set an SES light but even in dead of winter (ha not so cold or long here) with 180F I have heat pretty quick and no problem holding ~180F.

Our montana friend has a feature article on his web site that take all the mystery out of what works for cooling.He found the 195's pushed the temp over 212+ before they were fully open. He recommends & uses the RS 180's. Now with the new screw on marine pump & duramax fan clutch & duramax fan blade the temperature swing problem is a past issue. Do you guys know the Duramax radiator is the same size dimensionally as the stock6.5 radiator ? It is!!! Stop the wide temperature swings ,stop the block cracks,I say!!!

Can't help with a pro or con comment however I recently upgraded my fan and clutch and it was recommend by the vender that 180 F thermostats be used with this new setup. I've had the fan in for a couple of weeks, but I just installed thermostats today. I'm in Ontario, warm summers, cold winters, do people with trucks in the north run the 180's all year, or do you have to change them out as the weather gets cold ? My truck had good fast heat in the winter with the 195's. Thanks

I saw that on the SS website yesterday when I was checking the price of the 180* stats. It sounds like you might be the guinnea pig for the 180 stats :) Are you planning on towing anytime soon? I'd be very interested to see if you notice a difference.

My truck heats up nice and quick in the winter also. With some of the stuff I've read about the 180 stats, it has me a little worried about winter temps. I don't use a winter front but maybe that would be the solution.

Dave

Our montana friend has a feature article on his web site that take all the mystery out of what works for cooling.He found the 195's pushed the temp over 212+ before they were fully open. He recommends & uses the RS 180's. Now with the new screw on marine pump & duramax fan clutch & duramax fan blade the temperature swing problem is a past issue. Do you guys know the Duramax radiator is the same size dimensionally as the stock6.5 radiator ? It is!!! Stop the wide temperature swings ,stop the block cracks,I say!!!


Are we talking about Heath? I can't find any articles that talk about 180* stats. Can you point me to the article you're talking about.

Thanks,

Dave

Even with 195's I can't keep my truck warm in the winter. I've been running 180's for over a year now. The only benefit of 195's in the winter as far as I know would be that the heater blows hotter air. And if you can tell the difference between 180 and 195..your a better man than me :p:

I could be wrong though, so I take no responsibility for this response :D
Jay

Remember that t-stats control the MIN. operating temp. not the max, thats up to the rad and the rest of the sys....

My 180's caused no ill effects in the winter or otherwise.

I believe running 180 therms would cause greater temps swings than 195 therms. as KGT says the therms only control the min temps not the max. The max temps will be the same between the 180 and 195 therms. I believe it is the sudden temp swings that is the greater threat of cracked heads and not contiuous high temps. You can only heat and cool metal so many times before having trouble, the greater the temp swings the sooner you with have it.

The vast majority of every engine manufacturer recommends 195f operating temps and thats what they have been designed to run at.

The max temps will be the same between the 180 and 195 therms.

I tried hard but you are going to have to explain this one to me...........

I believe that using the 180 gives the cooling system a 15 degree headstart on keeping everything under the max temp. I run 2 RS and have heard the Factory dual stat run one of each, I can't verify that but I thought that might even give you the best of both worlds. My 95( before I sold it) love the 180's running right at 185-190 unloaded and 195-200 loaded. No big swings, temp gauge would get to temp and hardly every move. Before the upgrade and Rad cleaning I would swing from 190-220 with the fan clutch kicking in around 210 and pulling it back to 190 range.

It may give you a head start, but for how long, the max op temp is going to be what it is no matter where you start from, you start from a stone cold engine and the max is still gonna be the same. now the max operating temp is controlled by the rad and its ability to shed the heat from the hot coolant passing through the core and the ability of the fan to draw it throught the rad when req....

Looks like this thread is going to end up in another "clean your radiator" argument.

I do not care what you guys say. I take my radiator right out of the truck and clean it properly. That is the biggest problem with cooling on these or any other trucks. I know this for a fact, I drive a diesel highway truck for a living and if you do not keep the radiator clean it overheats too! I am 100% sure that my radiator does not control the operating temperature of my engine in any of my vehicles.

Quote: Jasonsmack wrote: "I tried hard but you are going to have to explain this one to me."

The rad., water pump, and every other component in the cooling system is used to keep coolant temp down except the t-stat. T-stats are only used in a cooling system to keep the temp. up to a min operating temp., 180 or 195. If a engine is going to over heat to lets say 220f with 195 t-stat it will overheat to the same 220f with a 180 t-stat., a t-stat has no ability to make a overheating engine run cooler (except for a bad t-stat of course)

It may give you a head start, but for how long, the max op temp is going to be what it is no matter where you start from, you start from a stone cold engine and the max is still gonna be the same. now the max operating temp is controlled by the rad and its ability to shed the heat from the hot coolant passing through the core and the ability of the fan to draw it throught the rad when req....


Exactly, so max temp is determined by the ability of the cooling system to get rid of heat. If the engine is overheating to 220f on a hill, it will be with any t-stat that might be installed. The problem is the temp swing is greater with a 180 t-stat, there is a 40f increase and going down the hill it will drop very quickly 40f. back to 180f. But with a 195 t-stat you will only see a 25f temp varience. It is these large temp swings that will give the head a workout/crack not high sustained coolant temps.. (to a point of course)

Whoa, big guy. (talking to Jason).. actually, your rad DOES limit (not control) the cooling ability in all of your vehicles... but not because it's dirty, or because of anything you do. I pulled outta Brooks with Joann for a few years, and my KW got cleaned out lots, too.

I mention this because it ties in with the whole 180/195 thing...

Thermostats open up once their activation temperature is passed, and let the coolant circulate freely. From that point forward, it's a race... can the engine build heat faster than the rad can diffuse it to the air? If so, things cool off. If not, then the temps continue to climb until boilover - the heat input exceeds the cooling capacity of the rad.

When does that happen? That depends on a few things, too... the volume and heat-carrying capacity of the coolant (which is a good reason for using antifreeze in the summer) are factors because it ALL has to heat up, so more coolant = longer time, and better coolant = longer time. Another thing that influences it is the starting temp - when the thermostats open. With 180 therms, all that coolant has to heat up from 180* on... with 195s, all the coolant has to heat up from there. The end is at the same place, obviously.
The last variable is the fan - how much air it moves and when it kicks in are both factors, but the fan only gets into the game when the heat input exceeds the cooling capacity.

When you're pulling heavy and steady, the thermostats are only responsible for the bottom temperature, not the top... something we need to keep in mind when pulling hard into the wind or up hills... if it's heating up, and our rad and fan can't stop it, the only thing we can really do about it is put less heat in - let up on the foot feed, change gears, make sure the TCC is locked, etc.

When you're not pulling steady, the lower thermostats let the engine cool off to a lower temp between the hard pulls, which gives us a little more room to play with, but ultimately doesn't affect the whole thing.

The last thing is the continuing argument over temp swings, and I'm not getting into that one, other than to say the temp has already swung from 65*F to 195*F today... a 20* swing isn't that much, really.

Big truck, little truck, the same rules apply.

LOL... Tracy types faster than me.

I like your explaination better.

I am not saying switching to 180F thermostats is going to keep THE 6.5 from overheating in of itself only. In a runaway thermal load situation the radiator is the limiting factor. BUT......

A 15 degree head start is going to give an advantage cresting some hills. My EGT gauge leads my ECT gauge by minutes. There is some time delay for that 15 degrees to be made up.

I figure once thermostats open fully a surge of cooler water cools the engine and the thermostats modulate some more (maybe one or both and not sure how long depends on ambient temps and thermal load but I feel sure something is going on there). There is an additional time that the radiator then warms up and thermostats quit modulating and its up to the radiator to cool to its limits given the ambient temp. Then the fan warms up and engages and the system is at max cooling but unfortuneatly maybe up to 20 HP (I have read as high as 27 HP is robbed from the crankshaft but I think thats for gassers).

Just a few minutes difference at 55 mph makes a couple of miles of travel distance. No its not going to save you climbing the mountains but for rolling hills and smaller hills its going to help.

Over on the Page I saw news of a electromechanical fan engagement for the latest GEP Optimizer 6.5 or whatever its new name will be. IF the fan can come on as soon as the ECT in the head hits ~220F ??? or what ever I think its a headstart strategy in mind.

I think the 180 stat will allow your truck to overheat faster. The 6.5 is a heat producer and it will build 180 faster that 195 and the stat will open, now radiator can't disapate the heat fast enough as it pumps back into the motor from the radiator so the t stat stays open and in the summer no stat on the 6.5 is bad . I think the 195 allows the coolant to stay in the rad a littel longer allowing it to do it's job.
Mabe a bigger and better radiator is what we need.

Yep, I agree, Schiker. I'm not sure how much difference / time the 180 stats will buy you, though; maybe as you say, it's enough for the shorter pulls.

I also think the earlier-engaging fan clutch is a big thing, though... mine kicks in earlier, the temp stops climbing, and in most cases, comes back down.

I don't buy the 27 HP loss argument. Not because I don't believe it, but because if that fan doesn't kick in, you can't push on the foot-feed without heating up more, meaning you have a lot of potential horsepower you can't get to, anyway. Before I changed the fan clutch, I did the only thing I could do to keep the temps down... slow down, one gear at a time, until I was at 20mph in Bull-low. With my fan clutch engaged, I can continue to drive under power, uphill, with my trailer on the back. I had lots of HP before; what I didn't have was enough cooling capacity.



I am not saying switching to 180F thermostats is going to keep THE 6.5 from overheating in of itself only. In a runaway thermal load situation the radiator is the limiting factor. BUT......

A 15 degree head start is going to give an advantage cresting some hills. My EGT gauge leads my ECT gauge by minutes. There is some time delay for that 15 degrees to be made up.

I figure once thermostats open fully a surge of cooler water cools the engine and the thermostats modulate some more (maybe one or both and not sure how long depends on ambient temps and thermal load but I feel sure something is going on there). There is an additional time that the radiator then warms up and thermostats quit modulating and its up to the radiator to cool to its limits given the ambient temp. Then the fan warms up and engages and the system is at max cooling but unfortuneatly maybe up to 20 HP (I have read as high as 27 HP is robbed from the crankshaft but I think thats for gassers).

Just a few minutes difference at 55 mph makes a couple of miles of travel distance. No its not going to save you climbing the mountains but for rolling hills and smaller hills its going to help.

Over on the Page I saw news of a electromechanical fan engagement for the latest GEP Optimizer 6.5 or whatever its new name will be. IF the fan can come on as soon as the ECT in the head hits ~220F ??? or what ever I think its a headstart strategy in mind.

Uh, I'm missing something here, Joey.

The 180's can't allow your truck to overheat faster. The discussion is whether they give you enough extra 'climb-time' to make it worthwhile.

All a thermostat can do is set the minimum operating temperature for your engine. It's wide-open above that minimum, and only closes (to hold water in the block longer) when the engine jacket temps drop to that minimum.

The reason that 'no thermostat is bad' in a diesel is because the engine eill get too cool... optimum operating temp for a diesel engine is around 180-190*F. They get the best mileage there, they have the most power, they combust the fuel most completely... less than that and they don't run well.

You can't even set the injection timing on a 6.5 if the temperature is less than 180*.

As for a bigger and better rad, yep, that would work. More cooling capacity, more volume in the system, that would be a good thing. Some of the aftermarked rads are bigger, more cores, different alloys (aluminum, copper, etc), or different construction. It might also be a good idea to get some of the OTHER coolers (tranny, AC, OIL) out from in front of things.

I think the 180 stat will allow your truck to overheat faster. The 6.5 is a heat producer and it will build 180 faster that 195 and the stat will open, now radiator can't disapate the heat fast enough as it pumps back into the motor from the radiator so the t stat stays open and in the summer no stat on the 6.5 is bad . I think the 195 allows the coolant to stay in the rad a littel longer allowing it to do it's job.
Mabe a bigger and better radiator is what we need.

Uh, I'm missing something here, Joey.

The 180's can't allow your truck to overheat faster. The discussion is whether they give you enough extra 'climb-time' to make it worthwhile.

All a thermostat can do is set the minimum operating temperature for your engine. It's wide-open above that minimum, and only closes (to hold water in the block longer) when the engine jacket temps drop to that minimum.

The reason that 'no thermostat is bad' in a diesel is because the engine eill get too cool... optimum operating temp for a diesel engine is around 180-190*F. They get the best mileage there, they have the most power, they combust the fuel most completely... less than that and they don't run well.



My point is this, maybe I am wrong so lets see,
You just started climbing a long grade towing, now your truck is running at the 180 degree temps due to the t stat your running now it opens up and pumps into the radiator and the radiator dumps to the motor. Now the motor is working hard and is already 180 and climbing the water absorbs the heat as much as it can but now will stay in the block very little due to the lower setting of the t stat so it opens before the radiator can fully do it's job getting cooling off the water it just got from the motor. Now this may not happen in a minute or two but will happen quickly. The stat will remain open due to it's lower setting allowing the water to just keep flowing like no stat is present. Now all your coolant is the same temps and will only get hotter until you stop or crest the hill which even comes first.
I think a bigger radiator as well as an intercooler will solve it all for good.
Sound right or?

Joey ,The water pump could put a lot more water thru the engine WITHOUT a thermostat,all other parameters being the same.The thermostats are a restriction of volume by design. What do you think the difference is between the 78 GPM pump & the 130 GPM pump? Does the 130 GPM pump so much it can't cool? Your theory doesn't hold, well uh,water,IMO !!!

Joey D I don't follow that logic. If it works like that then once ECT gets to ~196-200F and a 195F opens fully I think it too would be "no restriction" and lead to a run away situation also. But in either configuration the ECT can cope with or recover from small ECT~10-15 degrees above thermostat temp w/o fan engagement.

I think earlier engagement of fan is big. In almost any temperature regulating system there is some gradient of temperature and it oscillates until steady state is reached. In stock trim if the engine gets so hot that fan needs to engage it has a headstart on overheating. And takes more effort to cool it. I THINK with twin 180F stats full flow is established earlier and the radiator can work a bit more before fan engagement. But over maybe what 197-205F ??? ECT either stat configuration is the same.

Hello all

I am in the process now of doing a complete upgrade on my 95's cooling system.
Along with the dual stat crossover there will be a set of 180F (RS) stats and then the fun begins

I have procured a new HO water pump for the 99 6.5 and tomorrow I am taking it to the pump rebuilders locally and we are going to remove the bub flange and replace it with the hub flange off of a Powerstroke.
I am then going to fit the Horton electromagnetic fan clutch unit that Navistar uses on the T444E.
This allows for manual fan overide as well as complete hookup and no slippage. (Has AC pressure switch as well as engine temp switch)

When pulling hard with a standard 195 stat the temps must reach 212F or?? before you have full water flow and then the gooooey drive fan clutch wont come on good untill about 220F by this time the thing is cooking hot.
If the fan is switched on during a hard pul or slow town cruising the cooling system can more and handle the heat.

The mods I am speaking of are easy to do as the PSD waterpumps are easy to find as junk and the shaft size is the same. .7455"
The bolt pattern on the pulley must be changed as well as the pilot diameter. A few minutes in the lathe and I will have the pilot fixed and then over to the mill to slot the bolt holes to fit the new hub.

The PSD fan hub is a 1.25" X 18 RH thread so all is well here for a direct retro with minimal bother.

Should really once and for all stop the issues of overheating.
The 6.5 will cool right down once you get the fan on, its just that getting it on soon enough is tough even with the HD clutches.

I want to keep it on when its hot and not have to wait for the gooooey drive.

Hope this answers some questions.

I will keep you posted as to the progress on this project.

MGW

Unless your radiator has issues the water speed is not increased by opening the stat a tad earlier.
The radiator can effectively cool the thing and keep it cool if you can get enough air pulled through it and there lies the issue.
The fan is always out of sinc.
Start the fan at the beginning of a long pull and then when the Stat opens there is plenty of cool water to work with as well as a heavy flow of air through the core to cool the hot water coming from the engine.

Timing is not an issue. The timing can be set at anything above 170F and the PCM will be a happy camper. Or if there seems to be an issue, stuff some cardboard in front of it to warm it up then do the TDC learn.

I still believe, having done the complete GM cooling update, that the dirty Rad. has as much to do with hot running 6.5's as any thing else discussed here, but we all know that part already right. I think the rest is just icing on the cake, so to speak.

Yep, I agree, Bowtie.

Under most circumstances, the cooling system can handle high thermodynamic loading, as long as the rad is clean (inside and out), the coolant volume and composition is adequate, the thermostat(s) is/are opening completely, and the fan clutch kicks in at a low enough temp with a high enough transfer rate.

The system is the sum of its components, and all of them are necessary. The one most commonly overlooked is the external cleanliness of the rad. Time and again, people swear their rad is clean, then freak when they remove it and see what's really in there.

For those who are overheating, and haven't yet pulled your rad to clean it, don't start looking for high-tech solutions to low-tech problems.

Or do so. Just don't ask me to validate that thinking.

TDCO setup at >170degf is to ensure PCM is not demanding advance due to low ECT - Base Timing must be stable when PCM factors OS position into the calculation - do the ko-ko routine and PCM calculates actual TDCO at that point at idle - use the scantool, rev the engine to select a number within the range of the IP at that position, as PCM attempts to kick in some advance for the increased rpm - it can't do advance in LEARN, of course, but you get the results as it tries.

TDCO setup at >170degf is to ensure PCM is not demanding advance due to low ECT - Base Timing must be stable when PCM factors OS position into the calculation.

Yep... as I inferred in the post this comment references, having unstable base timing would be a little hard on the fuel mileage.

Diesels LIKE being above 180*F. A hot diesel is a happy diesel (within limits, like most things)

Not perzactly - Base Timing is not effected by temperature, and will be unstable only if CPS or OS is failing - Advance is continually variable, depending on ambients, ECT, loading, driver demand, etc - therefore, GM does not want TDCO to LEARN if PCM is demanding advance - odd, that - they wrote TDCO DTC at ~1700rpm, rather than just above ~650rpm IDLE

OK... that little tidbit answers a few more questions; bottom line is still that 6.5s are most stable (? not the right word - they run best, etc) above 170*F

Sorta contrary to a gasser system, where cooler is better. (within limits, as usual).

clipped....
Unless your radiator has issues the water speed is not increased by opening the stat a tad earlier.
The radiator can effectively cool the thing and keep it cool if you can get enough air pulled through it and there lies the issue.
The fan is always out of sinc.


I look forward to reading about your current project. But I disagree with your first sentence. I think it works like this .... Normal operation radiator temp is something much cooler than ECT in engine (up north winter its probably stone cold) anyway stats modulate O/C to keep engine at operating temp. Now it gets even trickier with 2 at the same temp. I figure they modulate some each and can vary how fast and how much they open as they are not perfect digital switches. During normal operation (flat land) this water flow through engine and radiator is less than water pump flow. Depends on temps and how much stats open. Lets say its 30-40 gpm. Up comes a small hill.... EGT goes up dang near instantly with right foot. Mechanical time delay of thermal gradient ECT starts to rise, stats open more water flow increases to 40,50, 60 GPM as cooler water flushes through engine not sure how actual coolant at stats reacts but figure it averages some and one stat opens fully and you might get 90 gpm. If radiator is good and cool this flush of cool water makes the stats modulate some more. The radiator being bigger the surge of warm water disipates but warms radiator so next modulation of stats instead of say 100F water surges through engine its warmed to 110F. During hill climb after some circulating of water and radiator gets warmed up good stats quit modulating and you have full flow 130 GPM? 15 degrees cooler with 180's than 195's which is some time interval. So yes I think you do get full flow of circulation through radiator and engine earlier. Both radiator and engine cool better with the higher flow.

Pulling around here rolling hills this "headstart" seems to work for me as my ECT has never climbed to 220F + and engaged the fan clutch. It does climb up to 205-210F then comes back down as I crest the hill and can get back out of it.

I think coolant swings of 20-30-40 even 240 degrees F pale in comparison to ~1000F swing in EGT. High boost and EGT w/o intercooler hard runs and short shut down do way more damage to thermally fatigue the block/heads.

I agree except as I said the earlier opening of the stats does in and of itself not increase the flow rate.
The HO water pump will increase the flow to 130 GPM now the factory info says the flow increase through the radiator is only 9% over the original but the flow through the block sees the greater increase.

As far as how the two stats share the duty of the water flow I have no idea.
In theory if the water temp at the stats is the same they should open relatively close to one another.

The idea was to get more flow capacity and to allow for more water movement in the block.

The biggest issue with the 6.5 is the fact that there are some spots in the heads that the water stagnates in and this is where we see the "HOT spots"

I will say this. IMHO the HO water pump was and is a "BANDAID" for an issue that should have been seen during the first flow tests when these heads were modeled.

Now that said the HO is a good way to go and when the rest of the system is up to snuff this works fairly well to keep the little critters cool.

Lets look at the whole picture.
The cooling systems in our trucks have one real limiting factor and that is the ability to handle heavy heat load.
With the body style and size constraints therein one can only get so big of a radiator in the truck.

For example the class 8 trucks with a radiator thats huge and a fan the size of an airplane prop cooling is no issue (with a couple exceptions)

On a 100F day with my 500HP cat pulling 105,500lbs over a 7% grade for 5 miles the engine temp never gets over 185F with 180 stat in the thing.
The fan switch is set ot come on a 205 and goes off at about 170.

Now the Cat cooling system has flow through from the oil coolers that gets to the radiator even with the stat closed.

If I allow the fan to operate on auto control the temps will fluctuate up and down from 205F to 170/180 depending.

This same swinging with our GM trucks is not so easy for the cooling system to deal with.

Lets say we have a manually controllable fan and turn it on when climbing a hill, even with 195 stats (Dual unit) we will be able to maintain a reasonable egine temp without the ups and downs.

One of the folks over at TDP has installed digital temp sensors in the rear blockoff plate on his 6.5 and during hard pulls the temps there will reach 225 and some times more.

Another issue is the direct passage of heat to the coolant by the engine oil coolers and the tranny coolers.
The HD 3500 trucks have the engine oil coolers as a seperate setup.

The auto tranny can add some fierce heat to the coolant too that all has to be dealt with.

Having the engine oil and the tranny cooled via oil to air coolers will drastically help the heat issue.

Its all a compromise and the best solution is "Airflow" and lots of it.

I agree that having the engine at 195F will make for a nice complete burn on the fuel and also for better emmisions.

Unfortunately as the factory builds them the system does not work hand in hand to handle the heat load.

With the 180F stats and a controllable fan setup the heat should be quite manageable as long as one is watching the gauge.

The electromagnetic setup I am going to has controls that will do the management in auto mode. The fan on is 210 and off at 180. Now this is water temp and not air temp through the radiator.
Should prove to be quite a nice solution to an issue so many have toiled with.

The only reason you dont see it is the COST $$$$$$$

As I see it the class 8 trucks dont rely on the mickey mouse stuff is because it has issues and is not reliable.
Simple and if need be manually controllable = happy driver and happy engine.

MGW

My dual t-stat manifold\crossover was pre-owned, and as such had the oem RS stats @ 180deg and 195deg - the system is a constant-bypass recirculation system in a Diesel engine - apparent theory is : both t-stats opening simultaneously would shock the system with much cooler water, with possibility of block\head cracking, so the opening is graduated - the 180deg opens, allowing enough lower-temp coolant to mix with the constant-bypass circulation to maintain operating temps under normal loading - as coolant temperature continues increasing, the 195deg t-stat opens, reducing bypass flow - less resistance thru radiator than block - allowing more flow thru the radiator - as the oem fan clutch would probably not be engaged at that juncture, the coolant in the radiator is warmer due to the 180deg circulation, so the block\radiator delta is closer as the opening 195deg 'stat allows the additional circulation - intended to aid bypass flow in maintaining closer front-to-rear deltaT in the block and heads - system function hinges on enhanced operation of the fan clutch - lower-temp engagement has been proven to quickly reduce coolant temps under heavy loading service - towing, hauling, etc - DMax fan is thought to further enhance the system.

BTW - the late 5.9 Cummins pickups have the electric fan clutch, also

Are we talking about Heath? I can't find any articles that talk about 180* stats. Can you point me to the article you're talking about.

Thanks,

Dave

Heath recommends OEM t-stat, the last I knew.

OK, now I have a headache. Deltas, delta-ts, lambdas, omega moos! Just put one 180 and one 195 in there, If you're still over heating, and your rad is clean, you've got the big, badass clutch and fan and all of the other high speed, low drag gear, you need a super-duper radiator. Call Griffin or some other radiator fabricator, because you are seriously flogging your rig! It's not that complicated, if your system can't keep up, you need a bigger system. You can only move so much air and water before you're you're considered a boat or a plane.:D 5 pages on thermostats... I think we all need our meds adjusted.

ROFL - I believe you have stumbled upon the true issue, Rhino!

BUT - this is summer. Wait until November - I have a few predictions about what we'll see then:

This whole discussion will get resurrected, with "heating" substituted in for "cooling".

The thermostat discussion will be about keeping water in the block longer.

Finally, there will be an entire thread devoted to the fine art of cardboarding over your grille to keep the air out.

Next summer, we start all over.

Yup, I was already thinking about the heater thing, I just didn't want to bring it up.:rolleyes:

ROFL - I believe you have stumbled upon the true issue, Rhino!

BUT - this is summer. Wait until November - I have a few predictions about what we'll see then:

This whole discussion will get resurrected, with "heating" substituted in for "cooling".

The thermostat discussion will be about keeping water in the block longer.

Finally, there will be an entire thread devoted to the fine art of cardboarding over your grille to keep the air out.

Next summer, we start all over.


Hey get off the computer and get working on your truck! Trouble maker!! :D

Dave

You think this discussion is bad, DON'T go looking into the D-Max Overheat threads. You just don't want to go there, trust me.

I've had 180's since last summer....works good for me. I have a heath fan clutch going in hopefully this weekend.

Had plenty of heat last winter, never a problem.

I run them too, no problems.

Louis