my 97 integra has been overheating in town with the heater off but is fine with the heater on and overheats on the freeway after a while either way I already put in a new thermostat and flushed the system, all fans are in perfect working order any ideas what it could be? seems not to overheat as much in cold weather. I know the o2 heater is out behind the cat but it was out when my car dident overheat

 

Are you sure its not a faulty temperature sensor? Other than that your water pump might be failing or you have air pockets in the cooling system.

 

X2 ^^^

Make sure there is no air in the system, "bleed" it.

If the rad fan turns on and runs when engine is overheating but turns off before temp gauge indicates normal temp, the problem is either the temp. gauge, ECT sending unit or wiring between them.

A laser temp. gun will till you the actual engine temp. of the engine. 94