'07 6.0L safe max coolant tempurature while towing

Good afternoon guys.
Ok, I've a question of what upper end coolant temps the 6.0L engine will tolerate ?
'07 Chevy 2500 series 4x4 w/ auto trans and 3:73 gearing, 245-16 tires.

Here in the far norther reaches of California, Tehama County, we are faced with 113 degree days while towing a 7800-lb toy hauler from 350 el up to 6,500 feet asl.
There are three long hard pulls and on each one, I must drop the trans to low and run along approx 35-mph at 3,800-rpms. The temp gauge will sometimes get up to the 255-degree mark and hold.

I do wonder at what point I will experience an over-compressed head gasket, or maybe even stretched head bolts, _ _ or both ?

Anyone on the know of experience running the 6.0L engine to the 255* mark ?

thanks, Len

Greaser007 said:

Good afternoon guys.
Ok, I've a question of what upper end coolant temps the 6.0L engine will tolerate ?
'07 Chevy 2500 series 4x4 w/ auto trans and 3:73 gearing, 245-16 tires.

Here in the far norther reaches of California, Tehama County, we are faced with 113 degree days while towing a 7800-lb toy hauler from 350 el up to 6,500 feet asl.
There are three long hard pulls and on each one, I must drop the trans to low and run along approx 35-mph at 3,800-rpms. The temp gauge will sometimes get up to the 255-degree mark and hold.

I do wonder at what point I will experience an over-compressed head gasket, or maybe even stretched head bolts, _ _ or both ?

Anyone on the know of experience running the 6.0L engine to the 255* mark ?

thanks, Len

Click to expand...

The coolant itself is the limiting factor. A 50/50 Dexcool mix boils at 265ºF when fresh, so as long as you're not boiling the coolant, you're technically okay. If you do overheat, the thermal expansion of the aluminum heads will be greater than the iron block, which is how head cracks can happen. For comparison, cylinder head temperature red line on air-cooled aluminum aircraft piston engines with is between 460ºF and 500ºF, depending on the maker. Beyond that point, permanent deformation (warping) of aluminum alloy castings is likely, along with minor metallurgical changes in the cylinders and heads (accumulation of metal fatigue). So even at 255º, none of your components should be at any risk of damage or failure.

All of that to say that while you're technically fine, even if close to the margin, I would want to take steps to get that under better control, if it were mine. It would be best to start by making sure that the gauge itself is reading accurately by checking the data being generated by the sender in the OBDII data stream. You can also use a laser thermometer to check the temperature of the head adjacent to the sensor for comparison.

Also, several of us have found that our radiators have lost efficiency with age, for various reasons, so replacing it with a new OEM or Denso unit would likely help. Finally, I believe your cooling fan is direct driven off the water pump via a viscous clutch. Make sure that clutch is working properly.

I pulled a 7500 lb camper behind our 2012 Yukon XL Denali for years and have a whole thread here on keeping temperatures under control in the summer. Now I'm pulling it with a 2018 Suburban 3500 HD (6.0 gasser), and have had no problems with keeping the engine cool at all. It does have electric fans though. There are places here in the east that will rival anything out west for grade steepness and length of climb, but I have also pulled over mountain passes in Colorado and Wyoming with temps in the upper 90s with the Yukon, and never saw temps that hot. Makes me wonder if you have a radiator restriction, fan problem, or gauge problem.

@intheburbs will also have helpful perspective for you, I suspect.

Maybe its just me, but I would be highly concerned if l had temps of 215 or higher.

ScottyBoy said:

Maybe its just me, but I would be highly concerned if l had temps of 215 or higher.

Click to expand...

I get it. I used to think so too. But I've learned through experience and research that a coolant temp of 235ºF is common when towing heavy in the summer heat with these trucks. Hence the margin built into the coolant.

My little 5.3 engine towed a U-haul auto transport trailer loaded with my 1987 Cutlass for over 300 miles. Granted, we dont have any mountains here in Louisiana, its all pretty much flat. The highest I ever saw the coolant temp was about 215 or so, and thats only because I was going up the big l-10 bridge that crosses the Mississippi River in Baton Rouge.

Remember, too, that the pressurized cooling system raises the boiling point of the liquid. At my altitude plain water boils at about 200°F, so we are very careful to maintain the pressurized system and use the appropriate coolant to keep the boiling point as high as possible.

255 would definitely worry me.. I can only guess what the tranny temp was at that point.

230 I think I'd be OK with.

anyone remember the temp gm starts shutting down the ac and stuff? was it 260?

Fless said:

Remember, too, that the pressurized cooling system raises the boiling point of the liquid.
At my altitude plain water boils at about 200°F, so we are very careful to maintain the pressurized system and use the appropriate coolant to keep the boiling point as high as possible.

Click to expand...

So you're (likely) more aware than the 'average' vehicle owner about how important the pressurized reservoir cap is?
Maybe you replace your pressurized cap sooner / more often than, say, sea-level landlubbers?

j91z28d1 said:

255F would definitely worry me. I can only guess what the tranny temp was at that point.
230F I think I'd be OK with.

anyone remember the temp gm starts shutting down the ac and stuff? was it 260F?

Click to expand...

Anything over 221F, I stop driving like an @r$e and start driving like I'm about to pull over.
@ 230F I've already pretty much pulled over.
Just in case I forgot how old my reservoir cap is ...

(My tuner is letting me make changes to my tune regarding 'Hot' mode ...)

This is/was my "worst case" scenario...Pulling towards the Eisenhower Tunnel, ~10,500 ft altitude, 7% grade, 8600-lb trailer, 16,000-lb GCW. I was more concerned about the trans temp than the engine temp. But if you extrapolate the engine temp gauge, it's not even reading 230°.

255° engine temperature, is, to me, firmly in "something's wrong" territory, not simply "I'm working her hard."

Clogged radiator fins, corroded internals in the radiator, stuck thermostat, bad water pump, air getting into the system because of a leaky head gasket - all possible causes.

My 2016 Wrangler was running hot. Acting like air bubbles in the system. I'd purge the system, it'd run fine for a few days, then start getting hot again. It can bring up a digital temp readout and the last time it did indeed get to 255°. I did the indicator test looking for CO2 in the coolant - sure enough it tested positive. Jeep's in the shop now getting new head gaskets.

intheburbs said:

This is/was my "worst case" scenario...Pulling towards the Eisenhower Tunnel, ~10,500 ft altitude, 7% grade, 8600-lb trailer, 16,000-lb GCW. I was more concerned about the trans temp than the engine temp. But if you extrapolate the engine temp gauge, it's not even reading 230°.

255° engine temperature, is, to me, firmly in "something's wrong" territory, not simply "I'm working her hard."

Clogged radiator fins, corroded internals in the radiator, stuck thermostat, bad water pump, air getting into the system because of a leaky head gasket - all possible causes.

My 2016 Wrangler was running hot. Acting like air bubbles in the system. I'd purge the system, it'd run fine for a few days, then start getting hot again. It can bring up a digital temp readout and the last time it did indeed get to 255°. I did the indicator test looking for CO2 in the coolant - sure enough it tested positive. Jeep's in the shop now getting new head gaskets.

Click to expand...

Thanks for weighing in, Bill. Knew you'd have helpful perspective to share. So for the OP's benefit, here are the steps I would take at this point if I were in his shoes.

1. Verify that the coolant temperature gauge is reading accurately. Then, when the engine is cold, squeeze the upper radiator hose to feel the pressure inside. Take the coolant reservoir cap off to release any pressure and make sure the radiator is full to the top. Then put the cap back on, start the engine and rev it. If you feel pressure build up right away, that is likely a problem with the head gasket (not common on these). Pressure should not change much until the engine warms up. Make sure the fan clutch is working properly.

2. If that all checks out and he can swing the cost, perform a full refresh of the cooling system: Radiator, radiator hoses, heater hoses and plastic tees, water pump, thermostat, fan clutch.