Why is my daughters 97 Honda Civic EX Heater Blowing Cold Air?

This happened the other day when I went out to warm my daughters 97 Honda civic up one cold morning. I turned the car on, put the heater on full blast, locked the doors and went inside. After about 20 minutes, I came back out and the engine was hot but the heater was blowing cold air. Huh? It's not that cold outside...

So I do what I usually do when I have car trouble. I called my brother Chris who is a mechanic in Florida. He tells me to let the car cool down then check the radiator fluid level and if it is low, filler up.

So I checked the radiator fluid level, and yes it was low. The overflow was empty and as I looked into the radiator I could not see any radiator fluid. So I started the car, let it idle while I filled it up. Put the cap back on. Fixed, so I thought... My daughter had to go to school so I didn't have time to test it.

When she got back from School, and after the car had time to cool down I went outside to recheck the fluid level. Empty and so was the overflow bucket. So, I called my brother Chris again. He said to first check for a leak, so I filled up the radiator and started the car leaving the top of the radiator off. I turned the heater on full blast and watched the level of the radiator fluid which just stayed motionless as the car idled. It looked like the fluid was not flowing through the cooling system so I called my brother Chris again. It must be the Thermostat he said. So, I asked him does he think this is something that I can fix myself? Yes, a couple of dollars at the auto parts store and another gallon of anti-freeze.

Important. I am not going to walk your through replacing the actual thermostat but I will provide some helpful tips.

1. When removing the original thermostat, make sure you look at it as you remove it and make a mental note to yourself how it came out as you need to make sure you install the new one in the exact same position as the old one came out.

2. When at the auto parts store, make sure you purchase the gasket along with the new thermostat. If it doesn't come separately, make sure you open the box in the store and see if there is one inside the box. If not, ASK the auto parts store for a gasket.

3. After you have everything put back together, fill up the radiator and start the engine. Leave the radiator cap off and turn the heater on full blast. IMPORTANT: During installation you lost anti-freeze, you will need to keep filling up the radiator to force out the air bubbles. Even though the radiator looks full keep pouring in more radiator fluid, the weight of the fluid will force the fluid through the system. Trust me on this, it may look full but it's not.

4. Once all the air bubbles are out of the system and the heater is blowing hot air, fill the radiator overflow bucket up to the FULL LINE.

5. Dont forget to replace the cap on the radiator.

This cost me about $25 in parts, anti-freeze, and about 1 hour of my time to complete. Well worth it for a do-it-yourselfer like me.