My '97 Honda Civic overheats when driven at high speed on the highway for more than an hour.
I’ve changed the thermostat and the radiator fan, but it still does it.
Could you expand upon “when driven at high speed on the highway for more than an hour” ? How fast is high speed? Rocketman
May be a bad water pump (the vanes erode over time and lose pumping efficiency) or a partially collapsed/internally blocked water hose. I’d suspect the water pump.
Could be the radiator, is there a bunch of corrosion on the ends of the fins when you look down in the cap? Is there a ton of crap on the front of it? If no to either question, then it not the radiator. When it overheats are you driving at highway speeds? Low fluid, air in the system, water pump. If you are stopped and it overheats then you must check the fans are running, both if the A/C is on.
@kfenimore: It overheats when driving at highway speeds. Fluid is def not low. I haven’t noticed any corrosion, so it must be the water pump which is strange because last year I had a new timing belt installed so the water pump must be new
Check your receipt. Did they replace it? Still could be the system needs bleeding.
Start cheap and simple to expensive and hard. Check the air flow to the radiator (free). Bleed the system of any air (free). Next, change the radiator cap to spec ($10). Next, change the water pump ($65). Next, change the radiator itself ($75-100). Could also be brakes dragging, many other things. This easy to hard list is just what I’d try and in what order. Good luck! Rocketman
Does the car have an automatic transmission?
No, 5-speed manual
With the engine cold, remove the radiator cap. Start the engine and watch the coolant to see if any bubbles form in the coolant. If they do, it’s an indication of a breached head gasket.
There’s a chemical test you can use to test for exhaust gas in the coolant, might be worth a shot. I think Rocketman’s advice above is spot on, after verifying the coolant level is good, the coolant is in good shape and clean, and the fans are working, start replacing stuff, with the least expensive first. Even replacing the radiator with an auto-parts store replacement wouldn’t be that expensive. If you need some pro advice, instead of your mechanic, consider to take your car to your local radiator shop. They may can find the problem quickly, as they do this all the time. Best of luck.
Classic sign of a radiator cap that is not hold ing pressure.
If the radiator itself is not partially clogged then maybe there’s an issue with fan operation. You state that the fan has been replaced but not whether it’s operating as intended.
Engine temperature should cause the fan to cycle on at some point and operation of the A/C system should cause it to run all of the time.