ok so heres the prob....when im driving 50 mph or over my heat blows hot air fine. as soon as i slow down to 50 mph or below or come to a complete stop my heat starts blowing out cold air. ive changed the thermostat twice....ive drained and refilled the anti-freeze twice. now im thinking the water pump. any ideas????........also after a couple days of doing this itll start overheating.

 

check or replace radiator cap as well if you are not loosing coolant and have bled all the air out of your coolant/heater system.

 

you are probably very low on engine coolant check and see were the level is.or there is still air trapped in there.

 

thats the thing........ive already done that. but i noticed tonite that when i got home from work i could smell coolant but i cant seem to find a leak.

 

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Bleed the system first, then make sure the coolant sensor is working and the fans kick in , if the fan turns on then this is your next step.

make sure your motor is cold when you take of the rad cap fill it up to the brim with coolant if u see bubles forming at idle then guess what u need a head gasket....

and yes if you drive after a while and it starts to over heat or dump coolant

then odds are u need a head gasket , i know it sucks but i just went through exactly what your going through...... i thought it was water pump, changed that turns out it wasnt....

the thing is with a head gasket leak the combustion fumes can get into the cooling system and cause air pockets or bubbles whitch in turn causes it to over heat and dump coolant!

 

wow.....really hopin its not a head gasket but i never even thought about that....thanx that really helped.....but wouldnt that throw a check engine light????

 

NAh mine never threw a check engine light,,,

but ya i went a month bleeding it every 3 to 5 days i would bleed the sytem and it would run awsome as soon as 3 days cam by i was low on coolant, and if i went on the highway even worse the coolant would dump while i was on the highway and i could smell the faint sweet smell of coolant!

 

Your heater core may be leaking, clogged or both. That would cause you to smell coolant and it may only have coolant flowing through it at high rpms and speeds because it is clogged and the flow is restricted. You can try unhooking the coolant hoses to the core, then flushing it out with hot water. If the water flows in and out the core hoses youll know its not clogged.

 

I'm having the same issue and me it is a metal coolant pipe on the back of the engine block connecting to the waterpump ...They tend to rott out and crack...Same thing was happening loosing heat and smelling coolant... Might wanna check that out and it's about 70$ plus a 10$ O ring

 

Bleed the system as follows while using common sense and the appropriate personal protective equipment (safety glasses, gloves):

1. With the engine cooled down completely, remove the radiator cap.
2. In the picture I've attached below, you will see your ECT (Engine Coolant Temperature) sensor #1 to the left of the valve cover. Unplug it's connector and using a 17mm deep socket with a ratchet, remove the ECT sensor. Ensure you do not misplace the rubber sensor o-ring.
3. Top up the radiator slowly until coolant starts to pour out of the sensor hole.
4. Re-install the sensor, tighten it securely and plug the connector back into it.
5. Remove the reservoir bottle cap, fill the reservoir to the MAX line with coolant, the re-instal the reservoir bottle cap.
6. Top up the radiator to the filler neck then start the engine and allow it to reach operating temperature (the fans cycle twice).
7. Top up the radiator as needed during this warm-up cycle and one final time when the fans have cycled for the second time.
8. Re-install the radiator cap.

This is the process all of us use at the dealership to bleed the cooling system on the '01-'05 Civics and it works great. This bleed process also helps repair issues of gurgling inside the dash from the heater core .

Again, this is assuming you have performed troubleshooting for cooling system leaks, found none and that you have a properly functioning thermostat and no issues with the fans or fan control circuit.

If you perform this bleed procedure and you still have overheating issues, see if coolant is being pushed into the reservoir bottle (the bottle will keep filling up and there tends to be air in the radiator when you remove the cap). Often times a bad head gasket that is leaking combustion pressure will push air into the cooling system and forced coolant into the reservoir bottle. However, the engine could also be CONSUMING the coolant or leaking it into the cylinders, which after sitting overnight it will be difficult to start first thing in the morning but then run somewhat fine after. In that situation, it can constantly goes down both in the reservoir bottle and also the radiator and whether the engine pushes it out or drinks it, you will obviously require removal of the cylinder head to diagnose and repair it.

We had one customer who was diagnosed with a head gasket and it was discovered upon removal of the cylinder head that he had a cracked cylinder wall. So be sure to inspect that bottom end thoroughly when you have the head off .

Good luck!!!