Thread: Engine temperature fluctuating and running cold?

If it was me, I would have maybe changed the coolant aswell with the new thermostat and made sure all the air was out of the cooling system.

Maybe its possible there is still some air in the system? Or perhaps the temp sensor is acting goofy.

Originally Posted by jnnfr

Hi Everyone,

I am new here but have been having some problems with my engine temperature and was hoping someone here might have had the same problem or had some ideas about what's wrong.

I have a 2003 Grand Prix and usually it heats up to 90C after driving for a bit and stays there. It had only ever heated up a bit when I was doing a lot of stop and go on a busy highway which is normal. Lately, when I start my car, it starts heating up, gets about halfway between 70 and 90 and then spikes rapidly up to 100 and then back down to about 80. Generally the car is running at 80 now instead of 90 which I find weird. Not only that but when I'm driving around the temperature will fluctuate between 80 and about 95-100 randomly, but frequently. I thought at first that it was only heating up when I was idling and usually that's the case but I've noticed sometimes it fluctuates when I'm just driving around too, not stopped. I noticed as well that my heat in the car wasn't as warm as it usually is.

My first thought was thermostat so I got that replaced today but it still appears to be doing the same thing! My heating seems to be working better, but it's still running cold and fluctuating when I drive around. My mechanic seemed stumped and I didn't want to spend the money to have him poke around in there forever if he had no idea what it was.

Does anyone have any ideas?

Thanks so much!

what engine do you have and how many miles? i had the same symptoms with my car and it ended up being the LIM gasket.