I am at the end of my rope with my brothers car. It had an electric water pump on it and he started having some problems with it, so I swapped out the water pump to a new stock one and a new thermostat. Car has a brand new radiator. Here is the problem. The car will idle fine for 1 hour or more. You can drive it anywhere, then out of no where the temp gauge rises very quickly (under 30 seconds) to the red. On a few occasions right before it hits the red you hear a noise and the gauge drops to 180 in 2 seconds. I know for a fact the car is overheating. It is not a gauge problem. The hoses are ready to burst. Once the temp shoots down all of the pressure in the hoses is gone and it runs fine. only to happen again. I have bled the crap out of this thing. Would an air pocket cause this to happen?? The car has a manual fan switch and once the temp starts shooting up nothing cools it down. Does this sound like a bad new thermostat?? Thanks in advance guys, I am truly at the end of my rope.

Adam

 

I would test for a blown head gasket, (block tester or leak down test). A blown head gasket could be causing an air pocket to form in front of the thermostat, thus it is not able to sense the temp and fails to open. After awhile the air pocket clears and the T-stat opens. You could also try drilling a small hole in the T-Stat, this would allow the air to pass through. Also make sure you bleed the system really well.

 

Might possibly be the thermostat. Did you use the correct, long LT1 thermostat?

 

I am going to order a hypertech 160 today, keep the suggestions coming, this thing is killing me.

 

i have this problem with my car too...its always been like this...so i dont think it is a head gasket...i talked to GM and according to them...it is normal for the car to go the whole way to 245-250 and go back down quickly....thats just what they told me....

 

they are on crack, this is definately not normal

 

I had this same problem. I got a 160* Hypertech Thermo and did a computer tune from pcmforless.com Now it runs so low, like 175* Also check about your 2 Fans, it shouldn't go anywhere near Red.

 

Exactly, remind me to never go to that GM dealership... lol

 

think a 180* would fix the problem? my buddy has a brand new one he wants to get rid of...