superninja

I'm knew to Honda-tech so I hope I'm doing this right. I own a 2003 honda civic ex. The heater blows hot air when I'm driving but when I stop it blows cold air. I'm not very car fixing savvy but I like to learn how to do these things my self. My father in law said that it is the thermostat but my car doesn't overheat, in fact the temp gauge stays right were it should, so I thought it might also be my heater core. Can someone please advise so I don't blow $500 at my dealership!
Thanks
Mike

toyomatt84

iTrader: (1)

It could be your thermostat, heater core, or sadly... even your water pump.

2002-dxsedan

themostat is cheap, replace that, make sure your coolant is topped up aswell. if it persists let us know, we'll try again

Chiovnidca

My first thought would be checking the fluid level. Then bleeding the air out of the system. And go from there.

superninja

Thanks everyone for your helpful advice!!! My car has 145,000 miles and I have never flushed my heater core or any of my fluids except for oil. I will replace my thermostat and flush my heater core and cooling system then see if it fixes the problem. What is the best online resource to learn how fix the thermostat and flush my fluids?
Thanks
Mike

wwpotter

Superninja: thanks for posting this. Funny enough, i was literally signing on to the site to post about the same issue myself. I'll take the same advise and post back as well to keep the forum updated. Best of luck...

EY2002Si

I'm having the same exact problem with my '02 Si. My heater control valve works fine, I had the thermostat replaced, I bled the system of air, and I still don't have heat until about 4,000 RPM. It's not a blend actuator because heat will come through, and I don't have any coolant leaks anywhere. What the hell could be causing this?! Water pump sounds fine and the car doesn't go over operating temperature. It doesn't take longer than normal to warm up to operating temperature either.

jasmanda

I had the same issue with my 04 boosted EX with 105000miles on it. I replaced the thermostat and radiator cap, flushed the entire cooling system and cleaned out the overflow tank and hose and I have not had an issue since. Just make sure you take the time and get all the air out of the system, it took me a few times of driving the car around to get all the air out of it.

tjsker

My car has the same problem: hot to cold, cold to hot in a matter of a few feet of car movement.

The question I have in regards to a clogged heater core is this: If I am having hot air (when car in motion) then there must be warm coolant going through the heater core, so it can't be clogged can it?

Even if it's partially clogged there is no way the warm coolant in the heater core can cool down that fast enough to cause the heater to blow cool air after sitting motionless for a 30 seconds like my car does.

To me, the cold air has to be caused by the heater core that no longer has warm coolant in it. Now what would cause the heater core to drain at idle but fill up when the car is in motion?

tjsker

Forgot to post the resolution: Honda tech found the inlet hose going through the firewall was bent and was restricting coolant flow.

Vergilmr

have a 03 honda civic that runs hot intermittently I've changed the thermostat out. Changed out the fan cooling sensor.Replaced the coolant with honda coolant bled the system and the car ran fine for 2 days with no problems at all. Drove the car a third day and it ran hot and coolant in the overflow was boiling and coming from the cap. Top the coolant off since I lost some from the overflow had a technician come out and hook the computer up to the car and the fans would come on at 203 degrees both hoses were hot and the car would not run hot not while idled and with the road test. The technician left the computer hooked up and everything was fine...one of those situations where the car work fine when someone look at it. So the next day I drove the car to my parents house and I noticed the temperature gauge was climbing..I got to my parents house before the car ran hot. I popped the hood and the fans would not come on. I let the car sit drove it home the same distance and the car didn't run hot parked the car in the garage popped the hood and the fans were working with no problem and the car didn't run hot Today I drove the car and notice that the car blows cold air when idled or when I stop at a traffic light or stop sign..and when I take off driving the heat will come in. The oil looks good I don't see any white smoke coming from the exhaust or anything..and again I can drive and it runs hot then the next day it will be fine..please help. Im thinking it's a head gasket that is leaking but don't see any leaks..