The engine is starting to overheat now. Could this be a problem related to fuel mixture, the catalytic converter, or the O2 senser, or all three combined? I replaced the cat during the head installation b/c it melted. I've been reading where the wrong fuel mixture can create blockage in the cat and cause overheating. I am afraid the headgasket didn't go back on right or there is something wrong with the block. Would that cause overheating? I have replaced the radiator, water pump, thermostat. The engine is running like it got water in the distrubuter. I am not noticeably losing any coolant through the radiator.