i have a huge hole in my overflow tank, im getting a new one soon, but lately its been overflowing while it was boiling... i put a new thermostat in and a new water pump. i know the head gaskets are good bc i just got it bored out. anyone know?

 

rad cap?

 

From the comment about having it bored out, I assume you flushed out the system or at least had the coolant drained from the system. When you refilled it, you probably had some air trapped in the block and when the engine got hot it started bleeding out. I had that happen after I drained and flushed my system. It looks like it is boiling but it is actually trapped air escaping.