[TRICK_5_0]

I have a 306 with everything done! my cooling system was never a problem with this combo, recently ive been having high pressure in the system, and the flow is not proper and the temp fluctuates rapidly climbing over 200 within minutes. I changed the head gaskets thinking the pressure in the system may have been cylinder pressure leaking in through the head gasket, but apparently that is not the problem, I also put a brand new high flow 160f thermostat. Any suggestions on this problem would be great!, Im thinking there may be a crack in the head or cylinder??, could this cause the problem??