Coolant temperature fluctuations normal??

Thanks for the feedback. I was thinking it could be air in the system, but I feel like the temp readings would be more erratic(?). Also, not sure about this but it just makes sense in my head… if the thermostat wasn’t opening and closing at the right time, wouldn’t the temp reading bounce back and forth on a constant basis? I was thinking fan as well, since the fluctuation happens during specific driving parameters… do the fans kick on at certain speeds or temps? I also noticed today that the temp SEEMS to be more stable with the ac running. Not sure if it’s in my head or not, but it seemed that way when driving today

Jman2 said:

... thinking fan as well, since the fluctuation happens during specific driving parameters ... do the fans kick on at certain speeds or temps?
I also noticed today that the temp SEEMS to be more stable with the AC running. Not sure if it’s in my head or not, but it seemed that way when driving today.

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'05 Electrical fan settings. If AC works properly, it lowers coolant temps a wee lil bit,
'cause 'Fan 1' is nearly always on if the AC is on and builds at least 220 psi.
'Fan 1' is 'Low Speed. 'Fan 2' is 'High Speed'.
Note how hot the 'High Speed' coolant threshold is.

If those temps are too hot for you, get tuned.

Marky Dissod said:

'05 Electrical fan settings. If AC works properly, it lowers coolant temps a wee lil bit,
'cause 'Fan 1' is nearly always on if the AC is on and builds at least 220 psi.
'Fan 1' is 'Low Speed. 'Fan 2' is 'High Speed'.
Note how hot the 'High Speed' coolant threshold is.
View attachment 443150
If those temps are too hot for you, get tuned.

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So based off of those fan settings, what I’m experiencing is normal? That would be awesome if that’s the case, because I was about to try to chase something that may not be an issue?

Does your 2004 Yukon even have electric fans? I think those engines still had the clutch fan.

If it does have electric fans, they are likely not OE, so you might want to verify that your fans are coming on correctly at around the specified temps.

How many miles? Is the radiator the original one?

Jman2 said:

So based off of those fan settings, what I’m experiencing is normal?
That would be awesome if that’s the case, because I was about to try to chase something that may not be an issue?

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GM is ... coerced by CAFE MpG scores to do things like
... specifying 5W20 in America, instead of 5W30 nearly everywhere else on the planet
... reducing the bore size and engine size for most pickup trucks and SUVs from 5.7L to 5.3L
... encouraging your transmission to upshift as soon as possible,
and to delay downshifts til you try to bury the throttle in the carpet

... raising fan-on coolant temp thresholds considerably higher than AC psi thresholds ...

If you take issue with what GM is coerced into making 'normal',
have your vehicle tuned.
Otherwise your vehicle will run hotter in stop'n'go, unless you use the AC.

Would be good to know if the system is electric fans or a clutch fan.

The coolant level was low……

Sooo, the coolant level is low now after trying to trouble shoot? Or low coolant was the cause of the whole issue from the get go? In either case, why was it low?

Was low from the get go. Purchased the vehicle, the oil pressure sender is out and the temp was fluctuating so I assumed there was an issue. Not sure why the coolant was as low as it was, I don’t see a leak so I’ll be monitoring the level.

Before you make this complicated make sure its full of fluid. Air in the system can cause temp fluctuations