Coolant temperature fluctuations normal??

[Jman2]

I just purchased a 2004 Yukon. Noticed while driving that the engine comes up to temp and holds around 190-200. Once on the highway, when accelerating around 50-65 mph the coolant temp rises from 210-230 range and then drops back down to the 190-200 range and holds at highway cruising speeds of 60-75 mph. Is it normal for coolant temp to fluctuate like this? I’ve never noticed the temp needle move in previous vehicles once the coolant reaches the operating temperature.

 

[SilverSport]

the gauge on the instrument panel should be water temperature...

 

[Marky Dissod]

I just purchased a 2004 Yukon. Noticed while driving that the engine
COOLANT
comes up to temp and holds around 190F-200F. Once on the highway, when accelerating around 50-65MpH the
COOLANT
temp rises from 210F-230F range and then drops back down to the 190F-200F range and holds at highway cruising speeds of 60-75 mph.
Is it normal for
COOLANT
temp to fluctuate like this?
I’ve never noticed the
COOLANT
temp needle move in previous vehicles once the
COOLANT
reaches the operating temperature.

1. Only Corvettes get motor oil temp sensors.
2. Even if accelerating at Wide Open Throttle uphill, unless also towing something HEAVY,
coolant temp should seldom if ever exceed 221F.

I'd check the entire cooling system piece by piece. Feel free start by replacing the coolant reservoir cap,
then work your way up the parts + labor costs.
(Fire parts derringer before parts magnum before parts desert eagle before parts rifle before parts cannon.)

 

[Jman2]

Corrected the post to show coolant temp

 

[Jman2]

Are there specific components that may be more associated with the symptoms described?

 

[tagexpcom]

How warm is the ambient temps when you're seeing this? 70F is one thing, 100F is another perhaps.

I'm no mechanic but in my experience, it should hold steady once it reaches the top temp. Seems like a competent auto-shop can answer this question definitively. I like the advice above to start working on the system piece by piece. Temp sensors/gauge 1st then thermostat perhaps (and flush the coolant) and after that things should be clearer - e.g. the only thing left would be radiator / hoses unless you have something really serious like oil in the coolant (cracked block).

 

[Jman2]

It’s happening in 50-60F ambient temps, which is why I’m somewhat worried. Not sure how high it would get in hot conditions. What’s weird is that it only reaches those 220-230 ranges on the highway while accelerating around 50-65 mph. Stop and go traffic hovers around 190-210

 

[Fless]

I'd suggest picking up an OE thermostat at the OE temp, and changing that out. When you pull the current one out, see if it has an opening temperature stamped on it. If the new thermostat has a jiggle pin it should be oriented at the top of the thermostat, as installed.

 

[strutaeng]

That's a little high reading. I can usually see the temperature needle move a bit, assuming it's the thermostat opening/closing. Like a tickmark +/-.

Hook up a scanner that reads live data and see what's showing up on the ECU side vs. cluster.

 

[tagexpcom]

Another thought. Fans are electric these days. Our 2004 Cadillac SRX started overheating in stop-go traffic (big city interstate type stop-go) but would be fine the rest of the time, back home at smaller city traffic. Turned out it was the fan not running at low speeds but fan was running OK at higher speeds - so prolonged low speed/hot day would cause overheating. I was told it was a frayed/broken wire? - simple fix and been good since.

So maybe a fan / controller issue while accelerating?

 

[Jman2]

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

 

[Marky Dissod]

... 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.

'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.

 

[Jman2]

'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.

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?

 

[Fless]

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?

 

[Marky Dissod]

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?

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.

 

[Fless]

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

 

[Jman2]

The coolant level was low……

 

[afpj]

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?

 

[Jman2]

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.

 

[NardDog]

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