ok i was driving my car on a long trip 2day and its a 1990 accord 4d dx model and its started overheating the wierd thing was i downshifted to third and gained speed and it started to run normal temp but as soon as i put it back into fifth gear it started to heat up again any help would be appreciated it has a new thermostat all new hoses and a new heater core and radiator is what i replaced but the guy i bought from said it had a new headgasket

 

If there's pressure at the upper radiator hose right away from a cold start up, that would be a defect headgasket because of pressure from the cyl leaking into the cooling system.

Also, it can be your radiator fan that might cause it to overheat cause it's not working when it should when the coolant temp gets to a certain temp. The ECU turns on the radiator fan to cool the radiator by watching the ECT sensor if I can remember correctly. But usually when the car is moving on the highway, it shouldn't overheat though if its a fan issue.

Does it overheat when you're at a complete stop then goes back to normal when the car is moving again(around 50-80mph)??

 

no it overheats when im cruising at like 60 mph but if i downshift into third gear and take it up 2 90 mph it cools down for a lil while and then heats up again

 

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