My 2002 Honda Civic has an overheating issue after I drive it for about two hours or so. It burns through my coolant at a really fast rate without any signs of a leak. I've so far replaced the coolant cap, thermostat, and already checked the fans but they were good. I haven't seen any signs of my head gasket being bad. My water has been clear without any discoloration, it just recently passed the California smog test without any white smoke coming out, and I can still drive it when it over heats if I speed up to about 30 or, put my car in park when at a red light. I have no idea what it could be and would rather figure it out before I take it to a mechanic shop and possibly get ripped off.