Hi. I just got a 1996 Chev Crew Cab with the 6.5. So far so good. I'm only towing a 5000 TT so I hope not to have any problems with overheating. The engine looks totally stock.

It's been 3-7c (37-45F I think) here lately but I notice my truck never really heats up. My temp gauge goes to about 85C (185F) and just stays there. Even when I tow my trailer the gauge never reaches half. Is this normal of should I be checking my gauge?

Thanks

Dave

At those ambient temperatures that is normal. You may see temperautres go up 5 or 10 degrees next summer on long hills, but if your radiators and cooler are clean 5,000 is nothing.
Take a look at my web page to see what I mean by clean.

even on a hot day mine never gets to 210, normal for me is about 195

Mine hardly budges unless I really step into it, then it will rise ~5 deg normally. If it goes 10 deg or higher I know something's wrong like low pressure on the coolant system.

Thanks for all the replys.. I've been told by several people that I need to do the dual T-stat mod with the water pump right away. I think if I'm only pulling 5000 lbs and my truck doesn't overheat I don't need it. What are yout thoughts on that?

Dave

drive it till it breaks and upgrade then. Keeping an eye on maintainence will keep it going.

My gauge varies between a little above the first larger marker and a little below the middle one. Apparently the thermostat opens and closes, and depending on the load, the water in the radiator gets cold enough to bring the hand somewhat down when the thermostat opens. When it steadies out, the hand is a little above the middle in between of the first and the middle marker. For the markers are distributed unevenly and the gauge is quite small, I cannot the temps --- the bottom low marker is labled 70C, the first larger marker is unlabled and the middle marker is labled 100C.

Dave, if your gauge MOTT shows a reading closer to the first larger marker than to the middle one once it steadies out when the engine is really warmed up, I think you should watch it closely because you might have a thermostat that stays more or less open all the time and should be replaced soon. I've had such a thing, it went barely above the first marker and took quite long to get there, and it was only on hot days when it got close to normal levels. It even sometimes worked and sometimes not, so it was very hard to tell if was broken or not.

Exactly right Olee.. My gauge gets to the first mark.. basicly 1/4 full (if compared to a fuel gauge). I do get heat from my heater but it takes a while. I think I will check it when it gets warmer out.

Thanks

Dave

Dave, your thermostat is broken. You should replace it as soon as you can.

Running the engine below operating temperatures due to a broken thermostat is a very bad thing.


PS: Replacing the thermostat is easy enough. Depending on the tools you have, you can either open the screws on the thermostat housing without removing anything else. If you cannot get at them, loosen the accessory belt and take off the AC compressor to give way. Four bolts hold the compressor on its mount --- if you take these bolts out, you can lift the compressor and put it somewhat aside. Do not remove the tubing that's on the compressor.

You should be getting a new gasket with the new thermostat --- make sure that you get it. Once the thermostat housing is open, take out the old thermostat and remove the remnants of the old gasket as well as you can. Do not let pieces of it get into the water lines. Keep in mind which side of the thermostat is the upper side so that you know that when you put the new one in. --- If you leave remnants of the old gasket, the new one doesn't seal and coolant will run out as soon as you start the engine.

Put the new thermostat in, install the new gasket and screw things back together. Check the coolant level --- some, but not much of it, will run out when you open the thermostat housing, so have some distilled water and maybe some antifreeze at hand to refill.

There's a bleed screw on the water lines close to the thermostat housing. You can open the screw and idle the engine some minutes so that water comes out of the bleed screw, then close it. When I did the replacement on mine, no water came out of the screw, though.

Drive around some, with the cabin heater turned on, then again check the coolant level.

It takes about half an hour or an hour to replace the thermostat. Just do it, it's cheap insurance.

I always have to put another 1/2 gal after I've refilled it. It has to get hot to let the last air out.

Thanks for all the replys.. I've been told by several people that I need to do the dual T-stat mod with the water pump right away. I think if I'm only pulling 5000 lbs and my truck doesn't overheat I don't need it. What are yout thoughts on that?

Dave
My thoughts are:

I hear this reasoning all the time. Then a year or so (the next summer usually) I get a call from the same party looking for heads. The temp you see on the gauge is the head temp at the LF corner. You cannot see the temps of the valve seat area, or cylinder walls...

My thoughts are:

I hear this reasoning all the time. Then a year or so (the next summer usually) I get a call from the same party looking for heads. The temp you see on the gauge is the head temp at the LF corner. You cannot see the temps of the valve seat area, or cylinder walls...I understand the that putting on the high volume water pump will move more water through the engine, but from what I understand aren't the heads different in 97? Meaning that the water passages in the older motor are smaller and that would be the bottle neck? Sorry if I'm wrong, but this is my first diesel.

Diesel or not I think they (gas and diesel) cool very much the same way.

Thanks

Dave

You are correct, but the flow would still be improved. I put the HO WP on this week. I won't notice:cool: any difference 'till next summer.

Mine heats up to slightly above 85 and doesnt really noticably move after that.

Also I started to notice that the heat is hardly warm at all, I guess its warm but its nothing compared to our other cars. And it was -10C yesterday and is only going to get worse! I want my heat.

The high capacity water pump was brought about to increase the volume thriough the block and push more through the heads etc. The dual stat manifold is also a key part of this setup.

What does the new manifold do?

The 6.5L cooling system is of the constant-bypass type - coolant is constantly re-circulated thru the block and heads until coolant temperature rises enough to open the t-stat, which passes coolant thru to the radiator.

The constant-bypass system maintains fairly even temps thruout the block and heads.
The indirect injection heads, with the pre-combustion chambers - pre-cups - inserted into the heads, are the main problem - requires constant hi-flow coolant circulation to remove the combustion heat retained between the valves and pre-cups.

The 92-96 system consisted of a dual function t-stat, where the closed t-stat allowed full bypass.
As the t-stat opened, it's secondary valve closed off the bypass, allowing full coolant flow thru the radiator.

Worked really well for 1/2-tons, but temps were un-managable on a working truck, resulting in blown h-gaskets, cracked heads, failed FSD\PMD modules, etc.

'96 got an improved single t-stat manifold, similar to the dual t-stat, without the bypass block-off.

Late '96 got an upgraded coolant system, with high output waterpump, dual t-stats and manifold with no bypass block-off, 9-blade fan (iirc), oil-spray-cooled pistons, and revised, larger coolant-passages between the valves\pre-cups in the heads.

The HO waterpump increased coolant flow thru the block\heads by ~75%, thru the radiator by ~15%.
The dual t-stats allowed for double the original coolant flow out of the engine and thru the radiator.
Maximum heat reduction in less time = manageable temps.

This was in preparation for GM's planned increase to ~215hp, including 1-point lower c\r pistons - which never happened.

However, the cooling system upgrades virtually eliminated the previous over-heating problems.

Installing the upgraded HO waterpump, dual t-stat manifold, and larger fan on a pre-'96 engine greatly reduces the probability of over-heating, even without the oil-spray and improved heads.

Try it - you'll like it......

Hm, sounds like a worthwhile improvement ... How much work does it require to install the upgrade?

Where's the bypass valve located? Can it be disabled, and would that make for an improvement?

New HO waterpump\gaskets
new t-stat manifold\gaskets\t-stats\o-rings
new upper radiator hose, required
new 50\50 antifreeze mix
Permatex liquid purple sealer - optional, but I like it, particularly around water\coolant-sealing gaksets

'96 owners - you may already have the new system - check it out

Water pump has HO just to the left front of top center, t-stat housing looks sorta pregnant, upper radiator hose faces driver's-side rearward

Ja, hm, how much work is it? :) For example, do you have to take out the radiator to replace the water pump or is it similar to replacing a vacuum pump, except that more parts are involved?

Remove fan and shroud - radiator can be left in place, but probably ought to be removed to clean area between it and ac condensor.

Always a trash trap in the '88-up trucks, you'll remove around a bushel of debris from that small space between - will make you wonder how it ever cooled.

Kennedy Diesel site has a pic of the '96 single-stat full-bypass manifold, and other tips.

Having just resealed the coolant crossover on the '96 and having done the WP too. I'd say your in for a solid days work.
Don't forget that you have to have the upper timing chain gasket too and it doesn't come with the waterpump.

And also if gm had run their timing 5 deg advanced of where it comes, put an open exhaust on it and given it full boost, even without an IC they would have had a better truck for sure. mine doesn't get hot towing since I switched the #6 piston.

Ok, a full day is what I was thinking of. I'll think about it --- maybe it's even the water pump that makes the squeaking I have :/

What about the timing chain (gasket)? All I know about the timing chain is that it shouldn't need to be replaced, but that it is a good idea to replace it once you're getting close enough to it.

I'll have to check out for a way to clean the radiator or at least the gaps between it an the coolers, still. The AC has been rather weak during last summer.

My truck gets hot when I pull my 6,300 lbs Camping Trailer up hill. It got hot pulling my K-5 Blazer over the Grape vine (I-5 north of LA) in July and I had to pull over to let it cool down. Towing my Camping Trailer in the summer I have to pull over about every 3 miles going up hill. The temp gets well over 210. I can tow from St. George, UT to Las Vegas in March both ways with no problem or major temp rise, but from Ceder City, UT to Navajo Lake is very bad. I cleaned out the pile of bugs from inbetween the radiator and a/c condencer and cleaned the vains of the radiator but it didn't help. I have a aux cooler but I havn't installed it yet. I think my thermostat is stuck open right now because the temp is low and the "service engine soon" light is on. The light goes out when the temp gets over 160. I like this truck but if I can't keep it cool towing up hill I may have to cross over to the Blue Oval. My first Diesel was a 92 GMC 6.5L Turbo reg cab HD 3/4 ton 4x4 w/343:1 rear end, 2,000 rpm @ 69 mph. It would heat up towing my boat up hill but not that bad. This truck I have now I think has a 410:1 rear end 2,000 rpm @ 58 mph and the temp shoots up fast when towing. I would like to try the aux cooler before I buy a $1,300 inter cooler. Does any body have any sugestions for me to help cool it down? Empty my truck weighs in at 6,972 and empty my camping trailer weight 6,300. I don't even want to know how much the combined weight is loaded down for 5 days of camping.

Troy,
welcome to the forum, go to FAQs at top of forum, a lot of you 6.5 questions are answered there, performance mods also help keep the truck cool, 6300 lbs not much of a load for 6.5. Exhaust, no cat, recalibrated fan clutch, deep trans pan, dual oil filters for a little better filtration plus extra oil to heat up are good cooling mods in addition to cleaning out radiator and ac evaporator fins.

SCE T-roy

Take alook at my web site and you will see how the new type thermostats can fail in the open position. You have already addressed the Bug in the Radiator issue which is very common with the new radiators.

You idea of atttempting to cool the engine through the use of additional cooler will not produce the results of an intercooler. Reducing the charge temperature will have a much greater effect.

If under the conditions you mentioned you are loosing coolant I would check for a bad head gasket before going much ferther. I pull a total of 16,540 lbs all over the country in all seasons at road speeds and never see 200 degrees.

T-roy, can you tell us what you've done to your truck, perhaps on a new thread? These engines don't sound or work the same once you get them "opened up" and making top power, nor do they make as much internal heat.

[QUOTE=HowieE]SCE T-roy

Take alook at my web site and you will see how the new type thermostats can fail in the open position. You have already addressed the Bug in the Radiator issue which is very common with the new radiators.

Howie. I looked at the pictures on your web site. Cool!

My thermostat is stuck open too. When yours was stuck open did your your truck over heat when towing??? It looks like that rubber seal stuck in the thermostat could cut the coolant flow in half. That could be my problem. I'm leaving next Monday for a 6 month deployment on the USS Carl Vinson CVN-70 and wont be able to remove my thermostat until July. Could you e-mail me a picture pointing out the location of the thermostat? whiteelk@lemoorenet.com I havn't had to do many repairs to these 6.5's and I have no idea where it is. I guess I could buy a book. Also, I have heard if you remove the turbo muffler you can hear the turbo whistle more. Does anyone know if that will cause any damage to anything?

so what temperature is the mark in-between the 160F and 210F on the temp gauge? my needle usually hangs just a little over that mark. i would figure that is 190F or so since the dealer i bought the truck at replaced both thermostats the day after i bought the truck because they went bad. i doubt the dealer would install 180F thermostats or would they?

steiner43511

The stealer most likely put in 190 stats since the Do Gooders have determined they are best for Snale Darter. If you intend to any heavy towing I would change them to 180s to prolong the head gaskets.

SCE T-roy

The stats on my page came out of a friend's truck. The truck would never come up to temperature while they were in there.
To finds the stat or stats, depending on the year of your truck. Follow thw upper radiator hose from the radiator to the top front of the engine. That small casting that the hose connects to is the thermostat housing. Open the radiator cap and drain a quart or 2 from the drain cock on the lower rear passanger side of the radiator. Now reove the bolts the hold the thermostat housing to the engine. Note the direction of the stats has you remove them Install the new in the same direction as the old and reinstall the housing. These stats are self gasketed so you do not have to use sealer.