1990 Honda Civic Overheating

My 1990 Honda Civic is overheating. I noticed it, in part, because no hot air was coming from my air vents when I was trying to defrost my front windshield. After I began driving, I noticed the temp was up near the red, so I drove it the short distance home. On the way, I noticed that if the car was in neutral the temp would drop. Also, occasionally the hot air would start coming out of the vents, but this did not last long. I haven’t yet done any more investigation or driving of the car. When hot air would come out of the vents, the engine temp would start to drop. When hot air was not coming out of the vents, cold air was blowing (as opposed to no air blowing). Any ideas would be appreciated. Thanks.

You’re describing the symtoms of an engine with a blown head gasket.

If there’s a breach in the head gasket between a cylinder and a water jacket, when the piston comes up on the compression stroke, air gets pushed into the cooling system. This air moves throughout the cooling system until it gets to the heater core. and that’s when there’s no heat from the vents. When that cylinder fires, hot gasses are introduced into the cooling system. This super-heats the coolant causing the engine to overheat.

Remove the radiator cap with engine cold. Start the engine and watch the coolant in the radiator. If bubbles begin to appear in the coolant, it pretty much confirms there’s a head gasket leak.


Thanks for the diagnosis, Tester. At least I’ll know that my mechanic isn’t lying to me when he probably will tell me the same thing. I’m assuming that this is not a do-it-yourself job (replacing the head gasket).

Not really. Open the hood of your car, look at the top of the engine, and everything you see has to come off in order to replace the head gasket.