Lexicon1

Ok, hope you can help
The temp gauge works, does not ever show overheating.
The overflow tank will boilover and overflow ONLY when I shut down the engine.
I replaced the radiator cap. Same symptoms.
The electric fan works when I put 12v to it, but does not seem to come on during shut down of the engine . This boilover seems to happen after I have been on the freeway and come to a stop and shut down at home.
I pulled the relay that controls the fan, I dont know how to test it. BUT, now that I reseated it, the electric fan will come on intermittantly, but not at shut down or when I think it should, eg: when I turn on AC.
So, should I replace the relay? How to test it?
Should I change the water sensor?
I dont think the thermostat is an issue since the engine does not overheat.
Help me with my logic.

Thanks for your help

MitchB

Most people don't realize that an engine actually gets hotter (in some spots) when you shut it off. (There's no more water flowing to cool it.) Hot spots that have trapped air will appear to boil the coolant as the air pockets get superheated.

So, I'd say that you have air in the system, which by the way, should purge itself out. And if you can't get the air out to stay out, you actually need a head gasket.

/Aerostar\

iTrader: (2)

Well first things first: flush and refill coolant. Always do this if you're having a coolant problem, most people dont do this nearly enough anyway. Then burp the cooling system to get rid of ALL the air, do a search for this, "burp coolant system" or "burping coolant system" or somethin, you'll find threads on how to do this, I know I said it somewhere and others have too. Thats all I have to offer, but good luck with the problem man, hopefully we can get to the bottom of this