I have a 2000 Nissan Altima with only about 115,000 miles, I know that's amazing low miles but that's true. I recentley replaced the thermostat. My daughter was driving it on the freeway and it overheated and she had to pull off the road. Later after getting it back home I determined a bad thermostat (it was stuck closed). I replaced it with one I got from NAPA Auto Parts (a Belkamp brand). I drove it for a few weeks and all seemed fine. However lately I notice that when you accelerate the car the temperature gauge needle goes down quite low from the normal range. Then when you let up on the accelerator the needle quickly comes back to the normal temperature range. Could I have purchased a cheap thermostat that is now stuck open? Or could the temperature sensor/sending unit be bad and I need to replace that? Or worse yet could I have a blown head gasket from when the engine got overheated in the first place?
The faster you're driving, the more cooling air is moving over the radiator. Slower means less air. For a 22 year old car, I would have replaced the thermostat, radiator, cap, water pump and temperature sending unit by now. Did you properly burp all the air out of the system when you put the new thermostat in?
Thanks for your suggestions. The radiator was replaced about 2 years ago. Why a water pump replacement recommendation? I did burp the engine after changing the thermostat, but maybe I didn't complete it thoroughly, I will check that again. Barring that, I will probably look at changing the temperature sensor.
Because it's 22 years old. How long do you think they last?
The issue is resolved. I cleaned the electrical contact on the temperature sensor and now it holds steady about halfway when the car is warmed up.
It could be a failing water pump
