Originally Posted by CivicSiRacer

Any of the coolant hoses expanding/ballooning? That is one sign of a bad head gasket. My coolant was fine when my head gasket was leaking. And no weird color smoke coming out of my tailpipe.
Also can try taking off the radiator cap (of course when the engine is cool), start up the car and set the heat to HOT (don't necessarily have to turn on the fans though). Let the radiator fan kick on and off about 3-4 times and watch the inside neck of the radiator (where you took the radiator cap off). If you see any bubbles coming up that is another sign of a bad head gasket (which happened to me).

Possible your thermostat is stuck closed causing pressure to build up in the system. Could be a bad radiator cap too (which is cheap to replace) - can try this 1st.