Engine Temperature fluctuations?

MARTHAJ0121

MEMBER
2016 GMC ACADIA
4WD
AUTOMATIC
106,000 MILES

Initial issue was flashing a/c with no cool air. Recharged and worked fine for about 2 days. Temperature erratic low. ECT sensor replaced. Temperature fluctuations higher than normal. Replaced thermostat. Still having higher than normal temperature fluctuations. Dealership says it's within normal range and can't find issue. Week later, a/c goes out again. No cold air. Back to dealership. No code, no issues, according to them. Temperature still fluctuating. I have had the vehicle for 7 years and temperature has NEVER went past 210° no matter the heat. I live in NC and average summer temp is over 100°. Dealership just wants me to pick up my vehicle but gives no explanation fir the inconsistent temperature fluctuations.

Wednesday, September 24th, 2025 AT 11:17 AM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi:

That is a tough one to answer without seeing the vehicle. However, if the coolant level is full and the thermostat is working properly, the next thing I would check is if the cooling fan is turning on when you reach a higher temperature, around 215°F.

Also, do you know if the heating happens in stop-and-go traffic and not highway speeds? Don't laugh, but will the heater produce heat at all temps, specifically when it gets hot? If not, it could even be low coolant or air in the system. It's just a thought.

Let us know.

Take care,

Joe

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Wednesday, September 24th, 2025 AT 8:26 PM

MARTHAJ0121

MEMBER
2 POSTS

Thanks for your reply. It will increase in temperature when putting strain on the engine, going up an incline or small hill, quick acceleration, or idling in traffic. At speeds under 50 mph, it usually stays 210°-220°. But, like I mentioned, it never moved off 210° for the life of the car, 9 years. They've assured me they bled the lines and we've also attempted to several times. At this point, they just seemed annoyed with me, but I sense another issue coming soon. They just found a leak in the ine from the compressor that's causing the new a/c issues but if I'm not running it, I would assume it wouldn't affect the temperature of the engine. Not sure if I'm hearing the fan kick on while I'm driving. Before all the issues, it was unusually loud while the a/c was on. Now, not so much. Could a dirty radiator cause it? Maybe the water pump? The heater seems fine. It blew hot air while bleeding the lines. It hasn't been cold enough to use it regularly, but it does blow out warm air. I fear we'll be replacing everything without finding the culprit

Thanks, M Delgado

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Thursday, September 25th, 2025 AT 2:35 AM

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

At any time do you hear the fan clutch kick in? Also, I would take a garden hose and under high press blow out the radiator and condenser cooling fins to help clean them off, please go over this guide as well. Here is a guide that can help.

https://www.2carpros.com/articles/engine-overheating-or-running-hot

If you don't hear the clutch fan kick in I would replace it with a OEM unit. Here is a video to show you how to replace it.

https://www.youtube.com/watch?v=PoVQpbkCvtc

Please upload pictures or videos in your response of any problems so we can see.

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Friday, September 26th, 2025 AT 8:43 AM