Ok, heres my problem. I have a 98 civic ex. Recently my civic started over heating after i've driven a while, like 20 miles. Then i stop at a light and it heats up. I turn the heater up and cold air is coming out. I give it a little throttle and hot air starts to come out. My radiator fan kicks on and it starts to cool off. I get home and my reservoir is full. I replaced the thermostat and radiator cap but it still does it sometimes. When im traveling at 65 mph on the freeway it doesnt overheat at all. Im kinda at a loss. My coolant is clean bright green and my oil on my dipstick looks great so ive ruled out a blown head gasket. Could it be i just got a bad thermostat? Maybe ive got air in my cooling system? I dont have a clue.

This all started like 2 weeks ago when i sprayed my engine down (to clean it) at a car wash. I dont know if that has anything to do with it or its just a coincidence.

Any help would be greatly appreciated.

 

Check level in the radiator itself, not just the reservoir.

Small leaks in the head gasket will push coolant out of the engine, but not contaminate the oil or make white smoke.

 

Ok, so when i pull the radiator cap and check the coolant level, what should i see? Or what should the level be? The last few times ive pulled the cap ive heard a gurgling noise like theres pressure in there being released. The radiator doesnt look full, but it doesnt look dry either.

 

If you're hearing a gurgling noise when you start to remove the radiator cap then you still have air in the system. Try bleeding the cooling system and see what that does for you. If you're 100% absolutely positive the cooling system has been properly and completely bled and air still seems to be getting into the cooling system, I wouldn't rule out a blown head gasket.

Also, in the future, use extreme caution when removing a radiator cap from a vehicle while at operating temperature as the 180+ degree coolant is under pressure and will spray out. It's best to let the engine cool down before removing the radiator cap.

 

Yeah i always wait for it to cool before i remove the cap, and it still kinda makes the gurgling sound. So what is the exact way of bleeding the system. I started the car with the cap off and heater turned to hot, and added coolant till its full. If im doing something wrong let me know. Thanks.

 

That's what you do. It must be done while parked on a level surface or with the front of the car uphill so the radiator is the highest part. If the car is facing downhill, air can stay trapped in the engine and heater.

The radiator should stay completely full to the top. That's what you should see next time you check it cold.

 

Thanks for the help guys. I'm gonna take it to have it pressure check on Friday. Hopefully not a cracked head. That would suck.