Topic: 97 Honda Civic heater issue

[Nicks92jeeper]

Well some months ago my heater in my car started to have some issues. The heater would work and not work. The blower motor is good. I checked the hoses going to the core and they are both hot. The radiator upper hose is hot and lower is a lot colder. I changed out the thermostat and recently when I did the head work, I changed the water pump. I can park my car on an incline with the cap off and bleed the system to get the heater working again. As soon as I shut the car off and start it the next day, the heater ill not work. Once in a great while I can smell coolant but only after I have added some after bleeding the system so I believe that is coming from the engine compartment. There is no fogging on the inside of the windshield. Radiator and the cap have been replaced as well as the majority of hoses. Water is in the reservoir. Oil in car is good and no mixing of coolant with the engine oil. I checked the wire driven valve that allows hot water into the core as well and that seems to be working well.

Any ideas why the heater can work at 100% and then not work?  Could I just not be bleeding the air out enough? Could the car not be getting hot enough to open up the thermostat?

Things that have been replaced.
Thermostat, water pump, radiator, almost all hoses minus a few small ones that go the throttle body.

[sharpxmen]

does it have a bypass valve? if it does check if it works (could be the reason both hoses are hot but it bypasses the heater core)/ also, some heaters have a thermostatic valve in them to help the engine come up to temp quicker (my stock camaro one had that) and if it's not working it could keep the water from coming thru.

funny, i just finished working on mine again (seems to be the project for the winter for some of us), fixed the cables that operate the heater doors (there are 3 of them) and manage to replace the foam on 1 out of the 3, the other 2 are impossible to get to unless i take the whole dash apart. I replaced the heater core last week and i could not turn the heat off anymore (at all), fixed the bent cables (straightened them) and got the doors to operate properly so they won't bend again. I still can't turn off the heat completely if i set the control on "defrost" or "heater" (due to the other 2 doors not sealing fully) but it's much better now and if set the controls to "vent" and "cold" would bypass the core altogether so that is i guess a reasonable alternative. I still want to put a bypass valve on the core so i can keep the heat out of the cabin in the summer.

[Nicks92jeeper]

Well I had pulled the dash when I had commented and when I was looking at the heater core box, I noticed a door between the heater core that either allows the air from the blower to blow on it or not to was broken so I removed it entirely for now. Monday I will be swinging into a salvage yard and grabbing a housing that should work for it and replace the one I have. I assume now that since I removed the entire door that heat will come out but not as much as it should since it is blowing on the heater core as well as through the other direction. This to me would explain why when I park the car on a hill, that I could get heat because the door would open up. Hopefully...

Another problem that I was having since I thought the problem as the heater core are the pipes that go into the heater core. The pipes attach by a clamp and seal with an o-ring. For some reason, no matter what I did hen I was reconnecting the pipes, they would constantly leak so what I did is put some water pump gasket maker around the mating end of the pipe going into the core and covered it in JB Weld everywhere to seal it even more. Tomorrow after it cures, I hope it seals.

[Jeffy]

Strange they have joints.  Most cores have the tubes brazed on.

[Nicks92jeeper]

It has been a pain in the @$$ as well. Why they went this way I do not know. The 96-98 model heater core was brazed on. This way is just a joke.

[sharpxmen]

most likely same core used in various models and just the pipes are different.

[Nicks92jeeper]

The core is exactly the same but different on the pipes. If for some reason the core I have continues to leak then I will be going with an earlier model core and modify the housing to fit it.

[neale_rs]

Could you have these tubes brazed on?

[Jeffy]

Could you have these tubes brazed on?

You would have to remove the o-rings and lets the solder fill up the gaps.

[Nicks92jeeper]

They are aluminum. Would that still be possible?

[sharpxmen]

you can braze it, you can also weld it if both the tank and the pipes are aluminum and not some alloy, although would be pretty close to the brazing of the tank to the core so i'm not sure how that would work (if it will affect that or not).

[Nicks92jeeper]

Well the core I have now is pretty much done and JB welded to death. If I get another core I will pry go to the earlier model core and see about modifying it to work. Then it is at least all one piece with the pipe fittings already brazed together.

[Nicks92jeeper]

Well the entire problem was the blend door. I put it back in but away from the heater core and taped it in place. Now the car heats up within a few minutes and all is well!