Purchased a 2003 Chevy 2500 4x4 6.0l with 103,000 miles.

Pulled my 24' stock trailer (empty) and the truck ran hot (up to 235, just a bit over at times then down to 215, 220, then back up to 235 etc...). When it had to work pulling up a hill, it always went up to 235.
Tranny temp ran at about 200.
Engine runs at 210 without a pulling a trailer.
Had a general "look over" by my trusty local shop - said fan clutch was going bad.
i replaced fan clutch with an extreme duty.
Flushed radiator.
Pulled stock trailer again (empty and loaded with cattle) and it still ran hot (same story, up and down, up to 235 at times)
After unloading, drove home about 100 miles with empty trailer, ran at about 215, could really hear the fan locking up (first time I really remembering hearing it loud) kept the temp at about 215 the whole way.
Replaced upper and lower hoses, replaced thermostat with a 165 degree thermostat, sprayed out radiator fins with power washer.
Drove to work today (no trailer), ran at 210 there and back.

Can't see it being a water pump - runs fine unloaded and on the way home.
No air bubble that I can tell, runs fine unloaded.
I thought it would have run at less than 210 with a 165 degree thermostat but it ran at 210, just like always...

Thoughts,

Thanks for the help!
William

 

Sounds typical. You would need an aftermarket radiator to see lower temps and electric fans. No advantage in running cooler. Your engine was designed and machined to operate in that temperate range.

 

If you are pulling it with truck in overdrive and not 3rd gear the trans fluid is superheating the engine coolant. WAAY to much weight to try pulling in overdrive. Especially if you are having to stay deep into the throttle while loaded. Does the truck have plenty of power and run good while unloaded?

But yes 210 220 230 nothing to sweat over with a LS engine especially if AC is on at the same time. Put a stock stat back in these motors work completely different than old SBC and BBC's

 

My fear is that if I really had a load (say a fiver) and were in the mountains, would it just keep getting hotter? I couldn't push it much more without having to stop.

Frustrating if that's the case.

 

Those kind of weights are in diesel territory a 6.0 will pull it on flat land where I'm at but damm sure won't be happy doing it. If you are in mountains or anywhere there are significant grades it's game over it's just too much for a 6.0. What kind of terrain and speeds are you driving in what part of us are you in.

 

It pulled the trailer great. I just sold a 5.9 cummins and was very pleased with how the 6.0 Chevy performed (except for running hot).

No significant grades. In southern Oklahoma, few hills but nothing the 6.0 chocked over. It would run up to 3000 rpms but not more. I've read where folks twist these up to 4K rpm's..., it would have burned up if I'd done that Saturday.

I tried running in 3rd (not overdrive/tow-haul mode) and made no difference whatsoever.

There is just no way the 6.0 should overheat with an empty trailer and strange that headed to OK (from Texas), in the early morning, it would run up to 235, but coming home in the hot afternoon(95 or so) it would stay at 215. I guess there is the possibility that it just doesn't like Oklahoma and was happy to be headed back to Texas...

Possible that the stat was sticking and by the time I had hauled two loads of cattle and started home, the stat worked its self free... Which is why I went ahead and replaced it.

I just can't own a truck that I can't keep cool and couldn't sell it to anyone else and maintain any integrity so I need to fix it.

Maybe it's not broken and 235 in southern Oklahoma with an empty trailer is fine but sure doesn't seem fine.

I'm not sure what I'm looking for but any other solutions are appreciated.

William

 

Your radiator might be clogged inside. I would replace the radiator . Sometimes you can't see the clog by looking in the cap. Is your fan shroud in good shape? A broken shroud could cause a problem. When you put the 160 stat in it should have ran cooler without the load. I have a 160 stat in my truck and on the highway it stays at 176 Degrees and every ls motor I have owned stayed at that temp with the 160 stat. At idle I have my electric fan come on at 185 and it never goes higher.

 

Tranny temps can't be 200*F because the fluid is adding heat to radiator, as noted in super heating comment above. That hot trans fluid is also cooking your trans. Next time it gets hot, check trans fluid temp w/ an external source & it will be much warmer (hot) than 200*F. Add an external trans cooler or add a larger cooler if truck already has one.

 

I had the same problem with my 2002 1500hd, would get hot pulling a 24ft enclosed when I hit a hill. Turned out to be a weak belt tensioner, belt was slipping when the fan clutch hit hard.

 

Thanks to everyone that has responded.

Concerning the new 165 degree thermostat - I assumed the truck would run cooler unloaded but it didn't, runs at 210 like always. Conclusion - stat is wide open and the fan clutch only locks up at 195 or so which lets the engine run at 210...??? Nothing magical about 210 - something is keeping the engine at that temp regardless of the thermostat which points to the fan clutch keeping the engine at 210. Yes????

Concerning the tranny - the gauge seems to work perfectly, runs below 200 unloaded, runs up just a bit past 200 loaded. It has its own cooler and seems to be very consistent. I agree that if the engine is at 235, it would seem odd for the tranny to still be only at a bit over 200 unless it's own independent cooler is doing its job...

Concerning the belt tensioner - certainly something to try - they are probably pretty cheap to buy...

Obvious that the cooling system in general just can't keep up when under load.

This could point to the radiator - but then why would it cool to normal unloaded - again nothing magic about 210... doesn't make sense to me...

Thoughts?

 

You said "w/ an external source"... how might I do this? I have a hand-held laser thermometer I use when baling hay - could I just point it at the tranny pan and get any kind of accurate reading as to the heat of the tranny fluid?

 

you will probably see 160s operating temp during the shoulder months when the ambient temp is under 60 degrees. You'd need to overhaul multiple cooling system components to see a lower temp otherwise.

 

So then my question is:

Should my truck, pulling less than the max towing capacity (10k), over relatively flat ground, in 90 degree heat, run up to 235 degrees?

If 235 is OK, then I guess I shouldn't worry about it.

My worry is that the next time I pull, maybe in 100 degree heat, it won't stop at 235 and I'll either damage the motor or be on the side of the road.

Having to upgrade stock components to pull less than the max towing capacity, over normal terrain just doesn't sound like the correct answer...

Would everyone here be ok with 235?

 

I had a 2002 Tahoe that was overheating in traffic, ended up being a weak water pump. Was the first water pump I've seen that went bad without leaking.

 

210 is stone normal and not considered hot for a LS they are designed to run right there. Trucks got a 100K on it next step install a new GM radiator that way it's guaranteed to be correct in form fit function and cooling capacity. The cooling fan is designed to cycle in at about 230-240 ish air temp not coolant temp behind radiator. If truck runs good and doesn't puke coolant after that it's just normal for that truck with the amount of weight on it.

Leave it in 3rd gear and you can wind it as high as you need to. Pulled more than a few trailers from south texas to and through colorado loaded in 3rd running 70-75 3500 rpm all day long literally. Loaded my big blocks usually ran 230-245. We've had a few customers comment heavily loaded their 6.0's run hot in about the same range and it been farmers. Every truck and towing situation is unique so it may just be how yours reacts. But again get a new radiator 100K miles who knows whats been through it coolant and debris wise its a safe cheap investment and you are already this deep into it.

I wouldn't sweat 235 at max load at highway speed in 90-100 degree heat.
Do you have a scanner to see what actual coolant temp is running not just a reading off the gauge. 03-04,05 had notoriously crappy gauge clusters and we have had all kinds of customer complaints only to find a gauge inaccurate right before the cluster takes a dump. I'd get a cheapie scanner if you don't have one and see what actual coolant temp is running

 

Thanks for the replies everyone!

Easy to replace the tensioner and the radiator. Will go ahead and replace the water pump while I'm there. Much much better than being on the side of the road with a hot load of cattle.

Thanks again for the thoughts, I'll post back once I pull a heavy load again.

William

 

Scanner is what I was thinking too. I have an 06 2500hd with the 6.0 and the temp gauge reads a hair under 210 all the time. Doesn't matter whether it's an empty truck in the winter or towing 7000+ lbs in the summer, coolant temp always stays the same. When towing, trans temp will rise to 2 notches under 200, but will drop a bit if I'm cruising on flat roads and the torque converter is locked. I always leave the trans in "D" not 3rd and use tow/haul mode. The trans won't shift into OD until 58-60 mph in tow/haul mode. Your truck probably has 4.10's, so towing in 3rd is keeping the rpm up, which can't be helping the engine temp.

 

I have a 2006 2500 with 8.1L and I know the engine temp gauge is not linear. The needle reads in the normal position just below or on 210, and engine coolant sensor can be reporting between 160 'ish and 220 according to an innova 3160 handheld.

regardless of thermostat the engine especially when not moving is going to reach 200 until the fan clutch or electric fans start moving air across the radiator. Heat rejection does not happen at the thermostat, it happens with airflow through the radiator. If you can try measuring the input and output temp at upper and lower radiator hoses you should see a significant temp difference, might give you some insight as to what's going on.
When towing you might also try running 93 octane opposed to 87, it should not be your overheating cause but I know mine runs better all around on 93.

other thought is do you have the fan shroud around the radiator? because that will greatly help airflow pulled through the radiator by the fan. fwiw my shroud was hitting my fan so i removed the shroud, this was before last winter and i also took the mechanical fan off the water pump, and i drove the truck all winter with no fan at all. i was in stop and go traffic for up to 15 minutes and never had an overheat problem, this was with outside temp < 60°F. i can't see your cooling system not being able to handle heat load from towing... or not being designed and sized to not on a 3/4 ton truck. one other thought is when you know the engine coolant is over 200°F and you know the thermostat is open, have someone bring rpm's up to around 2000 and then squeeze and hold the upper radiator hose and see if you can feel pressure and surge generated by the water pump, if not that may indicate a pumping problem with the water pump and lack of flow. but you have to do this knowing your thermostat is open. from what you describe happening it sounds like a classic stuck thermostat that won't open all the way, but you said thermostat was replaced... might be worth pulling thermostat and check it in pot of hot water.
...last thought is you said you replaced fan clutch, have you noticed a difference? can you tell when it kicks in? because when i bought my truck the fan clutch did not lock the fan to engine rpm's. after i replaced the fan clutch, when i run the AC in summertime the fan clutch now kicks in and locks very often especially when under 20 mph and heat builds up, you can't really not notice a mechanical fan clutch setup when the fan is turning 2000+ rpm with the engine, mine is loud.