Temp gauge going funky, Updated! Changed Thermostat but still does the same prob Options

[reko]

As i was driving on the highway on friday night i noticed that my temp gauge was almost at cold which isnt normal for a sunny summer day.

After rolling for 10mins, it went to normal temp. but started to go slowly from normal to cold back and forth 4 to 5 times after what it stays at the first 1/4.

It did it only once, but then on the next day, it did it 2 times and went back to normal.

Nothing happened yesterday, but still, i dont really like this.

I'm thinking thermostat, but who knows?

Is it bad? I mean I went to school today (which is about 20kms from my house)... should I change that tonight?

**UPDATE**
25/08/08: Changed changed the thermostat... The shaft bent so it was stuck open so I just put one for Camry since the one for Celica 2.2L didnt fit (dont know why but anyway....) Still does the same problem as before... temp gauge isnt stable...

So what's next?
Water pump maybe

This post has been edited by reko: Aug 25, 2008 - 5:47 PM

[Havok1997GT]

First off, its always best to go with the Dealer on parts like this. It may be more pricy, but you know your getting the right part brand new. Also makes it far less likely that the part is defective. Still possible, but unlikely.

Second,(and if im missing a part,step, or im just plain wrong about how this whole things works, please correct me.) the water pump just pumps the water, the thermostat is what regulates how much water it pumps. It reads the Temp of the engine, and cools as needed to keep the engine at normal Temp. Typically, with a bad water pump, its just not pumping to cool the engine, thus the engine over heats. If its running to cold its one of two things:

1, your thermostat is not working right
2, your gauge is broken

There really isnt anything other then that that could be causing a over cooling issue.

Again, this is my understanding. I havnt had to deal with many over cooling issues, lots of over heating issues, but not a lot of over cooling. But that is what you should be looking at as far as i know.