Have a 1989 honda accord DX. Replaced the Thermostat, heater core, checked the valve in the hose to the core that is manually operated from the switch panel. Stiil no heat. Could the water pump be out? Thats the only other thing that I can think of. the hoses in to the core are getting fluid but get do not get hot.

 

If the two heater hoses remain cool, then coolant is not circulating in heater core.

Are you sure the heater control valve is opening w/ the temperature control **** movements? I believe you have but wanted to be sure.

I would suspect you may have air trapped in the heater core. It can sometimes be difficult to clear. Have you bled air via the air vent on top of the engine w/ engine idling? If not try this.

If you confirm that all air is eliminated from cooling system, then heater core blockage may be a problem. Anyone ever install radiator sealant material? This stuff can sometimes block a heater core. Guess how I know!

You may be able to clear the heater core by removing the heater hoses and routing garden hose water to back flush the heater core. You need to figure out supply and return hoses. DO NOT APPLY FULL HOUSE WATER PRESSURE TO HEATER CORE as it is not rated for 40-50 psi and may burst. However, you can force water (always allowing some venting to prevent excess pressure) to backflow and should be able to clear an obstruction.

good luck

 

Took the heater control valve off and checked it out. Its working. It's a new heater core. I've bleed the line through the vent, that is if I've done it correcty. I open the vent, start the car and run it until fluid comes out a solid flow. Should I leave it open for a while.

 

I'll stick with this post....TX, might want to move your post here and delete the other.

When venting/bleeding the coolant is the cap off and adding coolant to be sure is stays full. Also the heater control valve should be open-max heat.
EDIT: Usually I have the bleeder open as I add coolant-before even starting the car-whenever I get into the cooling system---change t-stat, rad hose, ect....

There is a cable to the "air mix door", as mentioned by TX. DX so I'm guessing it has lever controls. Be sure it is moving as you slide from cool to hot. Also, Are you getting any heat when it is on defrost? I ask because there is another cable to the center vent (above the controls) that can come loose and get stuck in the "cold" position and blow COLD all the time-just had this issue last week on the 89 LX.

As the car warms up, make sure the hoses (in and out) of the heater core are getting warm/hot.

 

Thanks,
This all started when I was not getting heat. I thought it was the Thermostat. I replaced it. Still no heat, I took the hoses off the heater core and back flushed, Then I stated geting vapor inside the car. So I put in a new heater core. Major job. Have to drop the steering column and take out the dash. After I got that all back together still no heat. I then checked the valve in the heater core inlet. This valve is operated from the dash cold/hot lever. It looked like it was working externally but thought I better check it internally, so I took it off and it opens & closes when switched. The cable from this valve comes from the bracket on the air/mix door, both operate from the same lever. I'll double check to make sure the door is opening and closing. When I put the dash back in I thought I checked.

I keep the bleeding/venting valve open while added coolant until the level quits going down in the rad. and fluid was running out of the vent. Should I open the vent valve and drive it to see if any more air is in the system. If I just drive, as TX suggested, how would air in the system get out without the vent being open.

The cooling fans did kick on and the temp guage stays at the mid range. Did not think the fans were kicking on but they did finally come one.

Thanks for all the help. If you can think of anything else I would appreciate it.

 

Trapped air is circulated out w/ water movement and rises to top of the radiator, where it will stay. You may need to refill w/ coolant once air is eliminated,...if that is the problem.

If heater hoses are hot, then coolant is circulating and problem must be air mix door is blocking the heater core.

good luck

 

I too just put a thermostat in and it didn't fix mine. I get heat out of the heater if I let it idle in the garage for a long time, seems I get hotter air when I rev it up but as soon as I drive down the road she cools right down to almost cold air coming out of the heater. Very frustrating. So it is getting flow, is it getting enough flow though because of an air bubble.....Well maybe it's not an air bubble because it does get warm when idling so the air should have been out at that point. Is the water pump wore out? Fins bad?

 

tucknut-might want to start you own post, after searching. Also it would really help if we knew what kind-year, make, model, engine (YMME) you had.....the OP had a 3rd gen...your issue could be something else.....