Idles at normal temp, but when I drive off it gets hot

[SpThomass]

2006 GMC Yukon denali XL, LQ4 6.0

Weird little issue I’m having that’s happened three times now in the past two weeks.

It idles perfectly fine, specifically between 204.4-206.8 degrees, no matter how long I idle it. The issue I have is that the moment I drive off after idling it gets hot.

The two previous times it fixed itself, and brought itself down while in park again, but today it got into the lower 230’s. Yeah a little dumb on my end, but I wanted to see if it would sort itself out.

I had the entire cooling system checked and water pump replaced a few months ago, and during that time it had multiple head gasket tests and passed. Coolant is about an inch below the cool fill line, but that’s where it usually hangs out since I’ve bought it 3 years ago.

Weird little issue, I’m just stumped, any ideas?

 

[MassHoe04]

Do you have OE fan clutch or electric fans?

Is it possible the fan clutch is not engaging when operating temperature is reached?
A bad fan clutch may be spinning, but not kick the fan blades into high gear when needed.

It should spin at a reduced speed (still looks fast to the eye) at lower temps, then the clutch kick in into higher RPM when reaches set temperature.

After just a couple minutes, mine quickly reaches "around" 210 F and stays there regardless of speed or how long it idles.

 

[OR VietVet]

It has electric fans. Do you hear the fans or see the fans come on when idling? Turn a/c on to see if fans kick on. Check for air flow restriction in front of radiator.

Did you have entire cooling system checked and water pump replaced because of this problem or problem started after? Was the thermostat replaced with the water pump?

 

[MassHoe04]

It has electric fans. Do you hear the fans or see the fans come on when idling? Turn a/c on to see if fans kick on. Check for air flow restriction in front of radiator.

Did you have entire cooling system checked and water pump replaced because of this problem or problem started after? Was the thermostat replaced with the water pump?

OK. Forgot 06 went electric...

I like the area you are targeting here.
Maybe a wire, connector or sensor got damaged or knocked loose in the process of replacing the rest of the cooling components...

 

[B-train]

I'd like to add that air in a cooling system can make for erratic readings. Any time I do a cooling service, I run the engine to operating temp with the cap off and just let it burp itself and bubble the air out (you can also run the rpm up to 1500 or so). After a few thermostat cycles, shut if off and let it heat soak. This will give you your HOT reading. Top off as needed and cap it off. When it cools it will pull a vacuum on the system (providing cap seal is good) which will dissipate once its running again. I've used this in cars, trucks, and generators for 20 years and have had good luck.

 

[Donal]

Sounds like insufficient flow of air through the radiator and or insufficient coolant through the radiator. Just a lack of heat transfer from coolant to air.

 

[rockola1971]

Sounds much like the scenario with air trapped in the coolant system.