Just bought a Civic, heater issue
 

Hello, I'm new here to the forum. I recently purchased an 03' Civic with 110K miles. I searched high and low on here to see if there were a lot of problems with heaters blowing cold air and it seems to be kind of an epodemic with Civics. I have taken the usual steps to try and eliminate the obvious.

1. Topped off coolant level in the radiator and overflow at temperature..
2. "Burped" the system again, with the front of the car elevated, heater on high, and radiator cap off, plum full.

The car heats up extremely slow, so I suspected it may be a thermostat that is stuck open. Like yesterday, I let it idle for 30 minutes and the needle never moved at all. But oddly the heater was blowing hot air. On cool days, it only takes a few minutes down the road for the needle to settle on half way, so I know the thermostat is staying closed until temp then opening up. Funny thing is the heater blows ice cold air even at 4000 rpm. When I start on the frontage road and get up to 45 mph, in 5th gear, rpms low, it blows cold air, I can then slow down to about 30 at any rpm and it blows cold again. I am stumped. The valve controlled by the temp knob works also. Am I missing something obvious? Please help

Is it staying full? Park on level ground, wait until cold, then check in the radiator.

You may want to replace the thermostat anyway.

It was a little low this last time, but now after adding more coolant the problem seems to be worse. The stars have to be aligned right for the heater to blow hot air and on the way to work this morning I watched the temp needle move all over the place going higher than operating temp then diving back to the half way mark within seconds, while the heater was actually blowing hot air. I'm kind of at a loss at this point.

The radiator should stay absolutey full to the top. It sounds like your head gasket is bad, causing a bubble of air to form in the engine.

I was trying to avoid eluding to that conclusion. Is there any way that I can truly verify that it is the head gasket?

Does the water pump have a weeper on it to tell if it is bad? This is the first gear driven pump I have ever seen. Obviously new to me beings this is my first Honda. Car is still gulping coolant and heater blows cold air until highway. Oil is coolant free and I cannot smell coolant. Could it just be leaking into the intake, or exhaust? I see some white spatter around the water pump. Is it bad? I am trying to rule everything out before I change a head gasket. I don't even know if I want to tackle it.

I'm still adding coolant to the radiator every couple of weeks. I finally did a pressure check. I held, with no appearant leaks but still losing coolant? Could it be the cap, that heats up and leaks by just enough to create vapor/evaporation?

Sounds like a leaky HG, a very common problem in 7th gen Civic's. A lot of people have trouble diagnosing it in these cars because the normal symptoms (loss of compression, white smoke, oil in coolant) don't usually appear. Its probably just a pinhole leak and may be sealing itself once the motor gets warmed up.

Does the motor idle rough when you first start it in the morning?