*Normal* Cooling System performance or not?

[Bill 1960]

Question for you guys on whether I should take this as expecTed cooling performance or dig deeper.

Preamble: 65k miles / 10k hours on the truck. All original cooling system hardware as far as I know, but I think the hoses were replaced when Customs had it because the hose clamps were all non OEM when I bought it. I have flushed the system and replaced the DeathKool. Rad looks good. Prior to yesterday I’ve never seen the temperature gauge move off 210.
The trans is a fresh GM Reman. It has the OEM tranny cooler in front of the rad.
The truck is lifted and 35” tires bring my effective axle ratio down to about 3.3.

Yesterday, while doing a sustained climb on a mountain road, she went up to about 225 on the engine temp and 219 on the trans. Conditions were about 90 degrees F and the AC was cranking hard. I was climbing in 2nd gear ~3500 RPM ~ 60MPH and probably about 75% throttle. As soon as I crested it cooled down to the usual 210.

So, should I be concerned? Considering the lift and tires I’d say my truck is working harder than a stock vehicle, but not as hard as someone towing a trailer.

Thanks for reading, and any advice offered.

 

[OR VietVet]

Sounds normal to me when pulling up a grade, that gear and tires of that size, with a/c on and ambient temp at 90. I would be double sure that the air flow thru ALL coolers-rad/a/c and trans are clean for sure. The fact that it dropped down immediately tells me the system wants to work right.

 

[Geotrash]

Question for you guys on whether I should take this as expecTed cooling performance or dig deeper.

Preamble: 65k miles / 10k hours on the truck. All original cooling system hardware as far as I know, but I think the hoses were replaced when Customs had it because the hose clamps were all non OEM when I bought it. I have flushed the system and replaced the DeathKool. Rad looks good. Prior to yesterday I’ve never seen the temperature gauge move off 210.
The trans is a fresh GM Reman. It has the OEM tranny cooler in front of the rad.
The truck is lifted and 35” tires bring my effective axle ratio down to about 3.3.

Yesterday, while doing a sustained climb on a mountain road, she went up to about 225 on the engine temp and 219 on the trans. Conditions were about 90 degrees F and the AC was cranking hard. I was climbing in 2nd gear ~3500 RPM ~ 60MPH and probably about 75% throttle. As soon as I crested it cooled down to the usual 210.

So, should I be concerned? Considering the lift and tires I’d say my truck is working harder than a stock vehicle, but not as hard as someone towing a trailer.

Thanks for reading, and any advice offered.

Hi Bill, I don't see any reason for concern with that. It would be helpful to know the % grade, etc., but given that you were in 2nd, and that the TC doesn't lock in 2nd, you're gonna generate a ton of extra heat in the transmission fluid, which then gets removed from the fluid both inside and in front of your radiator, raising your coolant temps. Plus, at low forward speeds, there is very little ram air effect, so your fans will be doing most of the work of cooling the entire system. The Dexcool/water mix won't boil until 265ºF, so you still had plenty of margin there, and the transmission fluid is good until 270ºF before it starts breaking down. 219 on the trans is well within what GM considers the normal range. Modern synthetic Dexron fluid is really good.

Some things you can do to improve cooling performance with the stock system:
1/ Spray out the area between the radiator and the AC condenser, making sure all fins are as clean and free of debris as possible
2/ Make sure the fans are kicking on and up when they're supposed to
3/ Replace/repair the baffles on either end of the radiator to ensure that any ram airflow goes through and not around the radiator.
4/ Replace the thermostat if you suspect it may not be opening fully, but I suspect yours is working just fine.

 

[OR VietVet]

Can even get an old rad fin comb and make sure all fins are straight to allow better flow. It is amazing how much debris gets caught in all those fins for any of the coolers and creates hot spots across them.

 

[Sparksalot]

Thecopcar does similar things, either by itself or when pulling my 1500# teardrop. It freaked me out, but I’ve learned it seems to be inline with specs.

 

[Doubeleive]

I'm 50/50 on that, might be time for a fresh radiator or flush it and run some citric acid (radiator flush) in it for a couple days and flush it again.
question: why were you in 2nd gear? unless it was a short run I would just let the transmission do it's job, if you are trying to get around traction control/stablitrac then just pull the abs fuse.

 

[wsteele]

Another thing to factor in is the density altitude. As you gain altitude and the temps are up, you have a reduction in air density, so your cooling effectiveness is reduced. 90F at 5000' elevation versus 90F at sea level has a measurable impact on cooling performance.

 

[Geotrash]

Another thing to factor in is the density altitude. As you gain altitude and the temps are up, you have a reduction in air density, so your cooling effectiveness is reduced. 90F at 5000' elevation versus 90F at sea level has a measurable impact on cooling performance.

This is true, but the energy (heat) output of the engine should also drop along a parallel curve, assuming combustion efficiency remains constant, which is the purpose of automated airflow, mixture and spark controls. This is what happens with normally-aspirated piston-engined aircraft for example. The more altitude we gain, the less power we have and the less heat we have to contend with.

 

[Bill 1960]

I'm 50/50 on that, might be time for a fresh radiator or flush it and run some citric acid (radiator flush) in it for a couple days and flush it again.
question: why were you in 2nd gear? unless it was a short run I would just let the transmission do it's job, if you are trying to get around traction control/stablitrac then just pull the abs fuse.

I don’t know the percentage grade but it couldn’t pull it in third, it would just lose speed and gear hunt 2-3 if left in D. I’m going to SWAG and say 8-10%. Nobody was passing me.

 

[OR VietVet]

I really loved towing my off road rig with my Duramax. I was passing people all over the place.

 

[Bill 1960]

Thanks for all the feedback guys, sounds like a “feature, not a bug” LOL. I’ll just keep an eye on it. I can see now why people that are towing are doing cooling system upgrades.

So far the temp has been stable at 210 under all other conditions, whether it’s creeping up steep dirt or blasting down the interstate. I’ll update this thread if anything more happens.

 

[wsteele]

This is true, but the energy (heat) output of the engine should also drop along a parallel curve, assuming combustion efficiency remains constant, which is the purpose of automated airflow, mixture and spark controls. This is what happens with normally-aspirated piston-engined aircraft for example. The more altitude we gain, the less power we have and the less heat we have to contend with.

Good point, I think depending on the efficiency of the air fuel mixture control mechanism, the loss of horsepower (heat), might be more than the loss of efficiency of the heat exchangers. Although I will admit to the fact that pondering it kind of gives me a headache.

OK, for the forced induction crowd, ignore anything I just wrote. Cause you will get hotter.

 

[Sparksalot]

Thanks for all the feedback guys, sounds like a “feature, not a bug” LOL. I’ll just keep an eye on it. I can see now why people that are towing are doing cooling system upgrades.

So far the temp has been stable at 210 under all other conditions, whether it’s creeping up steep dirt or blasting down the interstate. I’ll update this thread if anything more happens.

Yep. I upgraded the transmission cooler to a Hayden 678 because of it.

 

[avalonandl]

With that many hours the water pump could be worn. Thats a weak point on the LS engines. I had to relplace mine on the 2005 GTO

 

[Foggy]

Thanks for all the feedback guys, sounds like a “feature, not a bug” LOL. I’ll just keep an eye on it. I can see now why people that are towing are doing cooling system upgrades.

So far the temp has been stable at 210 under all other conditions, whether it’s creeping up steep dirt or blasting down the interstate. I’ll update this thread if anything more happens.

Remember Also that if you are just reading the temp gauge on the dash, it's really ambiguous.
It will show 210* starting about 185 ish and stay there til about 215 ish....
It's so the soccer moms don't freak out

Your temps are normal.. Although I feel 10,000 hours at 65K miles is really really high..
Unless I read it wrong and it's only 1000 hour...
I bought mine with around 2500 hours and 98K

 

[Bill 1960]

Remember Also that if you are just reading the temp gauge on the dash, it's really ambiguous.
It will show 210* starting about 185 ish and stay there til about 215 ish....
It's so the soccer moms don't freak out

Your temps are normal.. Although I feel 10,000 hours at 65K miles is really really high..
Unless I read it wrong and it's only 1000 hour...
I bought mine with around 2500 hours and 98K

Yeah, I learned a long time ago about those “idiot gauges” the car designers use to save us from worry. I used my scan tool to watch the live data when I was cleaning and doing the coolant change and it was steady also.

This was a Customs truck on the Texas border. Probably never shut down at all during a work shift. Lots of idle time.