2012 Yukon XL Denali temperature creeping up at idle only.

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nonickatall

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I would do a co test of the coolant. Could be a damaged cylinder head gasket, which give pressure in the coolant. Than coolant is missing and your water pump cannot cool enough in idle. That explain as well, why your water pump is loosing water twice.
 
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ShakinNBakin663

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i would say make sure both fans come on. IMHO, sounds like the radiator is clogged, and doesn't have enough flow at idle. once you spin the water pump faster it'll force more coolant thru the radiator. Before tearing it out thoroughly inspect both sides, make sure there's no surface obstruction. But i'm sub'd for results
Both fans are operating at high and low speeds and have been confirmed by the shop. Radiator fins are clean.
 

Doubeleive

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Both fans are operating at high and low speeds and have been confirmed by the shop. Radiator fins are clean.
that doesn't mean anything other than visual verification
you still need to pull the connectors off the fan motor and look at it, the melting can be hidden and cause poor voltage/ground, so yes it may spin but may not necessarily have full amperage. easy to do just reach in and pull it off and look at it with a flashlight.
the internal function of the radiator can be poor as well even if it was flushed.
very few other reasons it would do this at idle unless the engine is clogged as well.
and contrary to what someone else stated I have not witnessed nor heard rumor of these engines "eating" the water pump, perhaps if straight water was used for years or it was never maintained period.
 

j91z28d1

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I agree a radiator is worth while.. I've changed out what seems like a perfect good radiator cooling wise, just physical damaged, with just a cheap 100$ auto parts store one and been amazed how much it helped.
 

Gearz

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This only happen to me one time in 30 years at a GM dealer after a coolant drain and fill. I could not get the air out of the engine so I remove the cross over bleed tube and it was plugged from the factory. I couldn’t blow air threw it so I ordered a new pipe and it solved the problem. The baffles are there for highway driving to direct the air to the radiator only and should be fine around town. Did you test the overflow tank cap and make sure it holds correct pressure?
 

petethepug

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If air is in the cooling system it will overheat. You can run the motor with the heater on Hi plus the rear heat on when the coolant cap is off. Without leaving the vehicle let it run for 20-30 min. Occasionally squeeze the radiator tubes to help burp it. Put the reservoir cap back on and take it for a spin.

If it begins to overheat at idle with the reservoir cap on, check the reservoir tank for cracks and leaks. Leaks in the tank will overheat the motor in a heartbeat.
 

retiredsparky

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Another thought: did the shop measure the actual fan rpm and compare to factory specs? Or did they measure the air volume (cubic feet per minute).

I agree with above postings regarding motor, temp sensor and ECM issues. When you say that the engine is idling is this only when vehicle is stopped? If the problem goes away when vehicle is moving with transmission in neutral and coasting to lessen engine rpm, then either the speed signal to the motors is too low at idle or the motors may be malfunctioning due to internal insulation breakdown. The”lacquer” (not really lacquer in modern motors) on the internal motor coil wiring insulation is very thin-if the coils gradually short out to each other, less power is available to turn the fans, even if the speed control is correct. The loss of power in the motor may not be detected by the ECM unless the current increases enough to cause a code to be set.

Replacing both of the temp sensors might be money well spent. Could there be corrosion at the harness connection to either of those sensors or to the motors?

If you have an infrared temp sensor scan the radiator for significant temp differences at idle. Cold tubes indicate a blockage. Check inlet versus outlet temps for comparison. This tool is also handy for checking bearing hub temps brake temps, exhaust manifold temps etc.

Have you checked for debris between the radiator and AC condenser coil?

Good luck!
Larry
 

retiredsparky

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Mr. Diver,
I get the intended pun-I have glowed once when a new Christmas gifted shirt with plenty of fuzz ignited from aluminum wiring sparking in a dimly lit room. As an electrician, I was doing a volunteer project for a retired Army veteran when his wife told me that my shirt was emitting an all over blue glow after shorting the hot wire to a ground wire. The shirt was saved, but my pride was somewhat damaged when she threw a towel on my shoulders. The words “You’re on fire!” got my attention.
In reference to the original subject, I also think that the coolant should be checked for combustion gases. I think the test kits are around $30.00, give or take. The test liquid that comes with the kit changes color when carbon monoxide is detected, I believe.

Larry
 

steiny93

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Sounds like an air flow issue (as when the vehicle is moving the issue goes away).

Since there was wiring damage and repair, have the electric fans been verified that they are moving the air in the correct direction?

Double check that they are getting up to high speed. From cold start the truck, let it idle and wait and listen for the fans to engage and speed up, write down at what temp it occurred.

If the truck is totally happy on the highway under load, seems to point to an issue with the electric fans.
 

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