Hey guys
I have a 94 EX manual with about 135k on the ticker. While i was driving on the highway today, i noticed that my temp gauge was almost 75% the way up. it never maxed out, but thats very abnormal since it usually is only 25% during normal driving....never going over the middle mark. But as i got off the highway and started driving slower (25-40), it went back down below the middle mark. and even at red lights it didnt go up! My experiences with overheating cars is that it happens more in city driving than highway driving. but my situation is the complete opposite. What would cause my engine to overheat only at highway speeds? im going to put some coolant in the radiator first thing tommorow...then see if it still has issues. oh, and there were never any coolant puddleson the ground where i park my car.any input or previous experiences would be great.
thanks!

 

Low coolant level (leak/s) or stuck thermostat (very likely). If coolant level is good, a new thermostat should be tried. Don't allow overheating as this can cause head gasket problems. Only use OEM thermostat for best performance.

good luck

 

I'm going to check the coolant and just replace the thermostat for the hell of it. its cheap anyway. and its probabaly the source of my problem. thanks man.

 

there is a good write up on our DIY section about overheating ,, I would suggest that you read it before you start replacing parts ..

 

checked the coolant level and its full. no leaks whatsoever. Got a new thermostat put in today....taa daa....problem solved lol. whew! thought it would be something more serious. So basically all it took was a $25 job. thanks to everyone that replied.

 

Thanks for telling us the final fix.

Some background from a heat transfer geek...
When driving at highway speeds the engine has to reject far more heat than it does in the city or idling. So on the highwaythe thermostat has to open wide to let plenty of coolant circulate to the radiator. On the highway there's more than enough air going thru the radiator.

OTOH, sitting still, the engine doesn't have to reject nearly asmuch heat *BUT* this time there's not much air going thru the radiator. So NOW the limit to heat transfer is on the air side instead of the water side.

SO... If it overheats on the highway, look for problems on the water side like a bad thermostat or a radiator that's got crud on the inside. If it overheats in traffic or stopped, look for reasons why the fans don't work.

But air pockets in the cooling system can cause confusing problems in either case. So that's always a good thing to check.

 

No problem.