My original radiator cap's seal went bad so it was leaking. I bought a replacement with the pressure release, but after driving, my low coolant light would come on. Bought another one without and same problem. Figured it might be an aftermarket problem, so I bought an OEM cap. Same problem.

I can start the car w/o the light on, and rev it, then the light comes on. It seems as though the cap is letting the coolant into the overflow bottle but not back in until it sits for a while. I can squeeze the coolant return line while holding the overflow line and verify that coolant is going into the overflow bottle.

The car now heats up quicker and on a recent 150 mile trip was running right at 220 on the HWY after about 120 miles.

I did clean the sensor when I replaced the radiator and haven't had any problems with it otherwise, so I don't believe it's the sensor.

Any suggestions?

 

Did you make sure there are no air pockets that need to be bleed out?

 

4 times.

 

were the 2 small hoses on the radiator hooked up correctly after the rad install?(overflow hose to the top port)

 

Yes. This wasn't a problem right after the radiator install. Around 3000 miles after the install, my cap started leaking. The seal inside was worn out. After the new caps is when this problem started occuring.

 

You may have to reset the light. I can't remember the procedure, but it's on shoebox's site I believe.

I never use the pressure release caps. Not worth it if that piece fails.

 

There is no "resetting" of that light as far as I know of.

Besides, the ECM's been reset about 5 times since this started happening, for other reasons unrelated to this, header install, etc.

 

Ok, I was thinking of the IAC. Could just be dirty or broken then. No big deal.

 

Did you make sure you bought an 18 psi cap?

BTW, coolant will not return to the radiator until the radiator cools, so the cap is not going to let coolant "back in" until then.

 

I understand how the system works, but as it cools down during hwy driving, it should let the coolant back in from the overflow and shouldn't let the coolant out right after being cranked up.

I'll go doublecheck the cap in a minute to verify the pressure. It was bought from the GM dealership, but I'm sure there could have been a mistake.

 

I can squeeze the coolant return line when the car's off and cold and feel it come out into the overflow bottle.

 

I tried re-bleeding today. I still have the same problem. This is frustrating me.

 

MHO, coolant is not going to go back into the radiator while the engine is at operating temp. The radiator would have to get considerably cooler than that for the cap to let it back in, because of the pressure.

Perhaps you have a leaking head gasket that is over-pressurizing the coolant and forcing it past the cap and into the reservoir.

 

I suppose that could be. Head gaskets were replaced 15K ago, but that doesn't mean they're not.