Coolant temperature fluctuations normal??

Jman2 · Nov 22, 2024

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 · Nov 22, 2024

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

Marky Dissod · Nov 22, 2024

Jman2 said:
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 · Nov 22, 2024

Corrected the post to show coolant temp

Jman2 · Nov 22, 2024

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

tagexpcom · Nov 22, 2024

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 · Nov 22, 2024

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 · Nov 22, 2024

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 · Nov 22, 2024

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 · Nov 22, 2024

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?

Coolant temperature fluctuations normal??

Jman2

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