still overheats

[Guest]

just put in a new thermostat tonight and it is still overheating on me.  it works good when im drivig but when it sits there and idles it likes to get hot.  also when it is sitting there the ses light will come on for a little bit then the temp will get up there to about 3/4 mark the fan will turn on and the temp will slowly drop then the ses will turn off.  whats up with this?  i do think it runs cooler on the highway now though it went from running just under 1/2 to running just over 1/4.  also is it possible to hear an intake gasket leak?  i can hear kind of a whistleing but it doesnt sound like it is coming from the airbox or from around the throttle body.  also one more thing is it possible to test a thermostat just in a boiling pot if water.  after i tool the old one out i put it in boiling water had the temp up to about 210 and the thermostat didnt open.

[1988GTU]

You had a rad flush right?

[Guest]

actually no i didnt. should that be the next step?  the guy at the shop never mentioned anything about it he just said try a new thermostat

[1988GTU]

When was the last time you did a flush?  If it was never or lonnnnggggggg ago...  Then it wouldn't hurt.

[Guest]

couldnt even tell ya when the last time it was done i juss got er a week ago.  i guess i could afford to have it flushed since i only paid 100 bucks for it

[1988GTU]

Sounds like a project car for 100 buckettes.

[96BlackRoseZ26]

I know this is kind of a late post, but how old is the car?  Have you tried changing the radiator cap?  If the cap leaks, and doesn't allow the system to build up pressure, that can cause them to overheat as well.

[rweatherford]

You say overheat, but what does that mean?  3/4 on the gauge could be perfectly normal without the AC on.

Yes the thermostat should have opened up in the pan of water.  I always test them before putting in a new one.  (Test the new one.)