test for head gasket:

run your hands in the exhaust. rub them together... are they damp? they should only be a little damp, you should not feel water on your hands. exhaust should _not_ be like the bathroom after you shower.

also, when the car is cold you can take the rad cap off and start the car. if there is a bad head gasket water will be very turmolous, possibly even spitting out of the radiator.

if you wait too long and you cook your car, guess what, you get to buy a new head...so be careful in your diagnosis.