I've replaced the thermostat, radiator cap, coolant temperature sensor and heater valve. When I have the a/c on the temp gets to 240-250. If I put it on high vent or heat for 15-20 seconds the guage drops back down to normal and I can put it back on a/c and the temp wont rise back up. If I turn the car off and let it sit for a little while, the process repeats. This only happens with the a/c on, without the a/c on the temp never gets over 210-220. Is there any other valves that could be sticking??

 

Have you ever flushed your cooling system? What type of fan do you have? electric or clutch

 

The radiator is about 6 months old, it has the single fan. I just ordered the dual 11" spal fans, they will be here Friday.

 

Did you flush out the engine block? A new radiator wont do any good if you have a lot of build up of rust and other junk inside the block. Check the water pump too. When GM water pumps go bad they usually start to leak water. Check it while its running.

 

If it was the waterpump or dirty block it would overheat all the time, not with just the a/c on.

 

normally, at least with my car, when i run the ac the car tends to run little hotter. If your getting poor circulation or the water pump is getting weak then that would make it really hot. And 210-220 without the ac running sounds a little hot too. But then again i have 160* stat.

 

my car use to overheat to 240 or so while sitting in hot traffic when it was stock and NO AC.. Fans dont turn on till high temps anyway as set from factory but 240 was ridiculous. I turned my heater on and the car cooled off....not sure why that happened. maybe it kicked a fan on early? i dont know

i since replaced the thermostat and programmed the fans to come on at a lower temp and its fine! rarely gets above 180-190 anymore

 

The car cools when you turn the heater on because the heater core is a small radiator. If you turn the defroster on it runs the a/c which forces the fan on at any temp.

Factory fan doesn't come on until I think 238°.

 

My fan turns on way before 238. My dual 11" fans from Spal will be in tomorrow. I have the stock 195 thermostat, should I run a lower one and buy something like the JET thermostat switch to make them come on sooner?

 

i took my thermo out and have never had another overheating problem since.

 

is the car act boiling at 240 it would be boiling bubbling making steam if not .check the act temp of the eng .running the heater should not drop the temp that fast it might help after a while i would check the sending unit and check act temp of eng most shops have temp check tools .i wouldnt take out the stat it will cause prob jwith fuel injection system run ritch

 

this happens because the water pump hoses go from the pump to the heater and back so it has more time to cool and thats why, because i took my heater and a/c out of my 1987 bir and thats what it looked like. so thats whats up.

 

160* t-stat here! no problems on the cooling except i keep filling the damn thing up. dont no where the coolant goes.....

but in traffic with the 160* stat, my block heats up to about 190. im still below stock which is good. i think.

im ging to say that your water pump needs care or your block flushed. when i bought my car it baffled me how it would reach 250*+ on interstate 15. The block had a family of dragonflies in it.... after the flush....it sticks at 160*