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Erratic temp Gauge 05' Buick Rendezvous

I have an 05’ Buick Rendezvous with an erratic temperature gauge when engine is hot and idle. When stopped in traffic jams, long stoplights or just moving very slowly for a long period the temp gauge shoots up very quickly creeps towards overheating then drops suddenly as a fan kicks in. Radiator fluid is full. I turn the heat on full blast to blow hot air off engine. Took it to the Buick dealer, they couldn’t find anything and welcomed me back if the problem came back. The problem is back, more frequent and happens in either hot or cold weather. Advice would be much appreciated! Thank you!

I am not sure you have a problem. That fan is designed to turn on when it is needed. , which is when the engine gets hot. It turns off as the engine cools. Sounds to me like it is working as designed.

Thank you for your quick reply. I’ve owned the car for 3 yrs and have not experienced this dramatic fluctuation in temps before. The car has always remained cool even while stuck in traffic for long periods. I live in the south and have traveled up and down the coast subjecting the engine to long drives and extreme temperatures. It’s always been great but one day last summer while waiting in traffic I noticed the car was near overheating. I quickly turned the heat on full blast and was able to start moving. Now the temp gauge shoots up and down whenever I have to let the engine idle hot for more than a few minutes. I don’t dare risk NOT turning the heater on (as a precautionary measure)when it occurs for fear of getting stranded somewhere far from home. I work out of the country, and will surely take it back to the dealer when I am Stateside next month. Just wondered if anyone had experienced the same behavior.

One Could Suspect Air Accumulating Or Being Trapped In The “Closed Loop” Cooling System. Purging The System Of Air, And Pressure Testing The System Could Be Considered.

Replacing the thermostat at that time wouldn’t hurt.

When was the thermostat last replaced and the cooling system flushed and the coolant replaced ?


I bought the car 3 years ago, used with 13,000 miles on it. I had the system flushed at about 30,000 miles ago. As for the thermostat? No idea. I’d guess it is the original. Very disappointed in this car. Power steering pump blew at 55K, fuses blow instantly if I try to plug in a portable air compressor, the engine gets hot while going up steep hills, the Check Engine light comes and goes periodically and now the erratic temp gauge. The car has 67k on it. I also own a 93’ Chevy work truck with nearly 300k and the thing never gave me a problem. Thank you, I will take your advice to the dealer along with my overheating car next month when I am back Stateside. Have a great day. CM