My 1996 Integra GS-R has been overheating pretty badly lately, I changed the thermostat and tried it without one and it continued to overheat. The electric fans are functioning properly and whenever I've changed the coolant there is no rust or muck in the radiator. The water pump is working, when I pull the throttle it seems to be pulling the water through just fine. The heater only blows hot air about half the time which looks like there would be clogs in the system, but the lack of rust/muck is boggling, has anyone ever heard of anything else causing these odd problems?