I installed a low milage 2.1 and it starts and runs well.  However:  the coolant boils up in the filler tank and gushes out the little tab(with the three little holes) on the top of the tank.  The heaters blow hot air for awhile then go cold(at which point I shut the engine off--never letting the temp gauge go too high).  Once the radiator got hot and I got some frothy bubbles out of the bleeder.  Other attempts had the filler tank overflowing before the radiator ever felt warm.  The only culpret I can think of is, of course, the thermastat, but it was working fine two weeks ago.  I have carefully checked all hose connections. I raised the front of the vehicle as per bently. Ideas?

Cheers,

Willy