I have a 2001 civic ex that overheats at highway speeds. Turning on the heater cools the engine. Have replaced the thermostat but no help. Fans run. There are no apparent leaks. Have burped the system. Radiator is full and collant bottle is at normal level. Any ideas?

 

When it starts to overheat, pull off to the side o fthe road and see where the coolant level is, on the resevoir. if its near the top, then you have a rather big problem. This sign is imminant so it make take a few tries to actually see if your coolant is high in the resevoir. Also, try looking through the recent past thread of overheating, in this '01-'05 civic forum. Do some research that way and see if you come up with any luck....

 

I'll try that. If the coolant reservoir is full, what kind of problem am I looking at? So far I haven't found anything quite like it in the recent threads but I'll keep looking. Thanks