I have a 1990 Bonneville and earlier this week I was driving back to school when I noticed that the temp gauge was starting to climb rather quickly. I stopped at a service station and saw that i was a little low on fluids so i refilled.

Continuing down the road the temperature began to climb and climb until it was about at the overheat point. At that time I revved the engine thinking maybe something in one of the hoses was sticking and when i got the RPMS to the 5000 point the temperature cooled down back to normal.

Now when I continued driving in regular gear every 30 seconds or so the temp would start to rise up dramatically again requiring me to rev the engine to 5000 before the temp would come down.

I can't figure out what the problem might be. I don't think that it is the water pump, because then the engin would have never cooled down even at 5000 rpms?

Could it be a false reading? The thermostat bad?

Any help would be appreciated.

i don't think so. Is it a hard job?

Its pretty easy ,2 things to remember after you loosen the 1 bolt ,when you take out thermostat housing be careful if it is stuck as I broke mine cause it was corroded and it is not a easy part to get.Other thing is it only has 1 bolt so when tightening you need to put pressure on other side prying down with screwdriver so it will tighten down flush or it will leak.If you do this it is an easy job.