Quote Originally Posted by Spyder
You mentioned that it is "full before you start it" which likely means it isn't full after it runs hot... which means it is getting out somewhere

replace the radiator cap, a bad one wont hold pressure and will do exaclty what you are having problems with. also check to make sure the place the radiator cap sits inside the radiator fill neck is flat..

I know you think the thermostate is in the right way but if it isnt it will sometimes not open fully or properly and will cause the motor to over heat.
If the coolant in the resuviour is boiling i wouldnt be suprised if it is boiling over...

With the thermostat... If he didn't get the proper thermostat for his oem temp range that could be causing problems as well.

get the cooling system pressure tested. Could be sucking in air although you'd be leaking fluid as well.