2001 Alero 3.4L Overheating
 

My '01 Alero is overheating. A little background info, last year I had a problem where the temp gauge was always reading cold. So, in December (2012) I replaced the tWhathermostat. Everything worked great...That is, until now. Now, my car is overheating per the gauge. On Friday (April 26) it overheated on my way home from work (to the point the red "dummie" light came on). I pulled off for about five minutes and then was on my way and the car ran at the right temp (half way point). The temp gauge was fluctuating pretty wildly on my way too work, and on my way home - from the half way mark up to just above the 3/4 mark on the gauge. When I got home, I noticed coolant lightly spraying out of the water pump. I replaced that today (Sunday - April 28) and that problem is solved. However, I let it sit idly in my driveway running and the temp rose to about the 3/4 mark and one lap around my neighborhood and it overheated again.

Something else - My A/C was working fine, then it would turn hot and then cold again. Also, today I let it run hot (with the red warning light on) for about ten minutes, expecting to see steam, or at least see/hear/feel some indication that it was hot. I could put my hand on the top of the engine (where it says 3.4L) and it was barely warm. I expected to feel the motor idle rough or something, but it was smooth.

What do you think it could be? I'm afraid (from what I've heard) that it could be a head gasket issue, but I'm not sure about that.

Also, the coolant temp sensor, if that was acting up, could that cause the problem?

When your car was running cold, your thermostat was probably stuck open. But you fixed that issue now. When was the last time you changed your water pump? Start, small and replace your temp sensor, its cheap and takes 10 min to install. Did you notice any leaking around your water pump area? Or a possibility is your thermostat is now stuck closed, but i would say no at this point because its about a year old.

Try the temp sensor to start. If nothing changes, maybe swap out your water pump as it circulates your coolant through the hoses and engine. Just did mine ,I picked it up for $40.00

Yes, I replaced the water pump a few days ago (I could see it spitting coolant out). Pretty easy swap out :) After I replaced it, I started the car and let it idle for 10 minutes or so and the temp did go up about to about the 3/4 mark on my gauge...Then I took it for a quick lap around the neighboorhood and it overheated (red warning light came on). It was not hot though (I could lay my hands on the top of the motor without being uncomfortable). I turned the car off, then I wiggled the temp sensor harness a little and after that, I've been running it for a few days now, and the temp fluctuations are minimal, and it has not overheated once. I think I'll try the temp sensor because it's only around $15 bucks so why not ;)

Thanks for the input!

How did it turn out?

I have not replaced the temp sensor yet - but the car has been able to control the temp without fluctuations and has not over heated on me at all for around two weeks now. I am wondering if by wiggling the temp sensor wire I was somehow able to re-seat the connections better - possibly corrosion? I don't know - very strange. I still plan on swapping it out, but haven't yet because I wanted to run it around for a while to see what happens.