When driving my temp goes up to about 275, no hot air comes out of the heat vents.. then it will got back down to around 200 degrees and i will get hot air out of the vents. I have a few ideas about what could cause this, but fig i ask for other peoples oppions

it is an 87 iroc carb

 

Could be air pockets in the cooling system. I wouldnt let it get to 275 though. Thats pretty hot.

Normal check list stuff though.

Is the air dam on the car?
Fans working?
Timing set right?
Car runs good?

 

The gauges in our cars are never very accurate. At a REAL 275 temp, you'd be boiling over I'm sure. So if your not boiling over, your not overheating. Try a new coolant temp sender and see if you get better readings - it's located driver side head between #1 & #3 spark plugs.

If it gets hotter when driving 35mph+ than it does idling, then you are missing or have a damaged air dam. It should be directly under the radiator. This is a very critical piece to the cooling. At a stop, the fans suck air through the radiator to cool it, but when driving above 35mph, there is no air flow to the radiator unless this piece is in place.

If the high temps happen like ... you start the car, leave it idle, it gets to what your gauge reads 275, then cools - all the while not moving anywhere - then I'd say your gauge is off (back to trying a temp sender), and what you are seeing is the coolant getting hot until the thermostat opens, then it starts to circulate through the radiator and cools back down some.

If a new sender still gives these high temp readings, I'd stop in any local shop and ask them to shoot the thermostat housing and radiator hoses with their infared temp gun and see what the temps really are. You might need a new thermostat (yours might be opening too late if the REAL temps are getting above it's rated tempurature before it opens). Factory rated thermostat is 195 degrees, you can go down to a 180 if you like, but no lower than 180.

 

Does the engine fan come on?

Sounds like air pockets to me but your gauge could be off badly. I have a fan switch that turns my fan on at 195* When it turns on, my gauge reads just over 220*. So, that said, I'd follow camaronewbie's advice first, especially if you aren't puking coolant all over like you would if you truly overheated it. It would be bubbling out of your overflow.

 

My T/A boiled over and shot the overflow cap off, and steamed everywhere when it hit 260*, so there is no way that 275* is accurate. It would be best to get an aftermarket gauge to see where your temp. really is.