I caught my car doing this once a couple of days ago. I looked at the temp gauge and it was on the red barely. Then it just shot back up to the middle of the gauge to normal. Just as I stated. this was a couple of days ago. I havent noticed anything too weird since then.
what could it be?
its 94 trans am
with a 160 t-stat.
any help would be appreciated.

 

Sticking Thermostat OR your low on coolant and it wasn't pumping coolant properly through the block because of an air pocket OR you have air bubbles in your system

 

air in your system was my first guess but usually you would see the same thing happen again if you didnt get the air out.

 

Check coolent level.. If its good, you probley have stuck thermostat.

 

Bleed the air out with the engine warm, and make sure coolant it to proper level. If it still does it, replace the thermostat as stated.

Dan

 

I agree, sounds like an air bubble.

 

I wanted to add that I had the car running in the garage after I came from work yesterday.
Once it got hot, the fans turned on but it took FOREVER for them to bring the temp to the middle 210.
but once im driving the temp is at normal.
weird!
Is it the thermostat?????
Or can it be the
Coolant temp sensor on the water pump?

I had a problem many years ago where only one fan would turn on and it wound up being the coolant temp sensor. I just dont remember if it was these same systems.

 

In my opinion, here is what happend:

As the car got hot, the radiator cap vented to the overflow tank hot coolant. As the radiator's pressure dropped, it created a low pressure (vacuum) and began sucking coolant back into the radiator until the pressure differential was mitigated. The coolant in the reservoir was probably at least 100* lower, and when it mixed, it brought the overall temp down.

You could have a sticky thermostat, but that's pretty rare.

My car did almost the exact same thing a couple of days ago. It was climbing to about 220, then I shut it off for about 1/2 hour, started it up, and within about 1 mile the temps dropped to <190. The next day I checked the radiator level and it was at the top. I checked my coolant and it was a little low in the reservoir. Topped it off.

 

This is where it starts. I got a feeling its low coolant or a fugged thermostat.

 

I checked the reservoir and it was dry!!!! I had flushed the radiator in the fall I guess I didnt fill it completely and never noticed because of the winter !
I topped it off with coolant and problem is gone!!!


Thanks to all of you for your suggestions!

 

Check your radiator levels too first thing before the engine is warm for the next few heat cycles. And keep an eye on the resevoir until its staying full in the radiator consistantly.