samuelriesterer

1998 Honda Accord EX V4 2.3lt

Car blows air but not very hot. Sometimes it may be warm but usually it is just room temperature, clearly not as hot as it should be. We just overhauled the cooling system with a new head gasket, machined the head, new water pump, new radiator, new thermostat. I even flushed the heater core with a garden hose. I know coolant is flowing because the temperature of the lower radiator hose is cold to start but warms up when the engine is hot. I also checked the two heater core hoses and both are hot when the engine is hot so I know hot coolant is going to and from the heater core. Just can't understand why the air is not hotter.

holmesnmanny

manually try to open and close the heater control valve

Robert Buehler

That is it for this thread. Dam it. I have the same problem and I am at a loss for what to try next. I really have a hard time believing water is not flowing through the heater core properly since I flushed with water in both directions and saw no debris and blew air through it last night. I disconnected the lines and ran a clean hose between the feed and return line and witnessed hot radiator fluid running through the hose. So what is going on inside that heater core that would cause no heat at idle but warms up at highway speeds.

The dealer has no ideas that impressed me so far. I replaced the thermostat and water pump so far.

I was going to replace the radiator cap today thinking maybe that could have something to do with flow through the heater core. I did notice it took a bit of bleeding to get fluid to return from the heater core. I would have thought all the air would have been pushed out without any problem but it took opening the flush cap for 10 or so seconds before fluid came out and the car had been running for a while. The fluid was hot.

I am at a loss

holmesnmanny

Warm the car up completely til the fans start coming on. Feel both hoses. Both should be hot. If not, push the valve so it goes towards the firewall. Then feel the hoses. They should both start to get hot. If they are hot, then it's possible the heater control door itself is either stuck closed, broke, or stuck partially open.

Treyschls

ac hot/cold blend door

Robert Buehler

Thanks for the suggestions, I thought about a blend door but I don't think the car has one.

I have worked the valve back and forth and when the system is working at highway speeds it clearly cools off if I close the valve. I guess it could not be all the way open in the first place but it sure seemed to pass water and air ok when I tried to flush it and back flush it.

I am beginning to think it is a minor head gasket leak that is creating an air bubble that is blocking the flow from the core back to the block. It is my worst case idea but I am out of ideas.

Actually I have one more and that is a small 12V pump installed in the line.

holmesnmanny

Its threads like this that make me want to give up helping people out.

You give specific detailed advice on a possible solution but the OP thinks they know more than you so they almost completely ignore what you say and try to tell you what the issue is instead.

Nevermind the fact that what they say has 0 percent chance at all of being the issue.

Kencatt

I've got a similar problem with a 98 2.3cl, recently not blowing hot air. I changed the thermostat yesterday and notices the heater valve cable was not moving with climate control hot/cold settings so I disconnected the cable from valve and manually opened the valve. Valve "looks" to be functioning OK with good tension and screw turning with lever.
Haven't flushed the core yet, what's the recommended method.. hate to damage the core inlet/outlet ports as its a tight squeeze?

Upper and lower radiator hoses are both hot as well as both heater core hoses.

Kencatt

Update.. Just drove the Acura to work about 5 miles and the heat started blowing nice and hot. Interesting thing is I took the car for a test drive (3-4mi to operating tempature) yesterday after install of a new thermostat (an manually opening the heater control valve) but the air was luke warm at best.

Robert Buehler

Not sure what you were trying to say but I'll cut an paste what I posted in another thread. It might help you understand the bigger picture.

Sorry if I am hijacking the thread but I have the same sort of problem and I cannot yet post new threads.

I have a 2004 civic hybrid with 325k miles on it. It runs perfectly.

So far I have never seen any evidence of oil in the coolant or water in the oil and the car is not blowing white smoke.

I have changed the thermostat, the water pump, the belt and the radiator cap.

I have flushed the system by installing two hose "t" fittings into the feed and retune lines to the heater core. The system looked very clean and free of obstructions. I blew air through the core and felt no restrictions.

I ran a clear hose between the two lines to watch for fluid flow and it was flowing.

I have checked the shut off valve and it appears to be open.

I have purged the system or tried to several times and ran it until it appeared to be very hot and still not enough flow through the heater core to generate heat at idle.

Last night it was not flowing coolant sufficiently through the heater core and I gave up for the night.

This morning I topped the radiator off (the overflow tank looks like it has the proper amount of fluid in it) and the heat worked at idle. WHY I do not know.

I ran the car for a bit, stopped for about an hour then checked the radiator and topped it off again. Then no more heat at idle.

Plenty of heat at 55 mph but again no flow through the core or very little at idle.

I cracked open the two caps on the feed and return lines to the core to check for air or flow. At first, I completely removed the cap an no flow pushing out the return. I cracked the feed and got only a little flow but then it began flowing. Both lines have the hose fitting caps so I though bleeding air out would solve the problem.

I am at a loss as to how water can be moving around in the motor without always flowing through the heater core if the lines are open. The car had just been running down the highway at 60mph with the heat working but then at idle the flow through the core drops down to almost nothing.

For some unknown reason there is insufficient flow through the heater core circuit. The core appears to be free of obstructions since it works from time to time or all the time at speed but only sometimes at idle.

I thought for sure the old water pump and belt were causing poor coolant circulation but after replacing them (the pump looked fine but thought maybe the old belt was slipping) still no heat. I put the clear line between the feed and return heater lines and had what looked like good flow and hot coolant. I blew through the core with my mouth and felt no restrictions. I hooked the line back up and idled the car for 30 min. and still no heat. The lines felt like they got warm but probably not warm enough since I had no heat. I checked for flow by opening the caps and it even appeared to have some flow. But no heat. Then this morning it worked. WHY. and now its back to only working at speed.

What is going on. Could it be a small head gasket leak that is keeping the flow restricted at idle?

this is where I am at now. I believe I have investigated all possibilities and would love to hear some more ideas. I realize that it is possible that some of the checks that I have done could be mistakes but I have thought long and hard about the diagnostic methodology and some results seem to confirm a working system or a none working system. So here is what I just posted in another thread.

Ok I broke down and ordered a 12 volt coolant circulation pump. It was the
Part #: REPA313514
AUXILIARY WATER PUMP, NEW

from Auto Parts Warehouse

Unfortunately they and other companies could not tell me what the inlet and outlet ports diameter was but I think it will be 3/4". This will likely be to large but that can be dealt with. The connection is a simple (+) and (-) so I think it will work.

My research if that is what you want to call it showed that many vehicle (mostly German) have coolant circulation pumps so this is not a crazy idea.

Actually since my hybrid shuts off when you come to a stop, I think a coolant circulation pump would have been a good idea.

I am still at a loss as to why the system stopped consistently flowing coolant through the heater core. If it is the head gasket it is not significant enough to affect anything else that I can see.

Please try to keep in mind that posts in these threads (including my own) are sometimes not as clear or complete as we think they are. Also the comments we all receive back are not always clearly understood. So if someone appears to be disregarding something you said, maybe they just did not understand what you were saying.

In light of this, can someone tell me for sure if this vehicle (2004 civic hybrid) actually has a blend door in the heating system. As far as I can see there is a dial to open and close the valve to the heater core and a fan control. The "Auto setting" seems to just increase and decrease the fan speed. So far the dealership service department has not been able to offer definitive advice but I am tempted to put it in there hands to see if they can figure out what is wrong. I am just worried it will cost several hours of labor and result in an idea and not a solution.

Robert Buehler

sorry I should have mentioned that I previously tried all of that. I would have just started a new thread with all the details but I believe this site makes you wait 5 days before you can post your own thread. I just jumped in on this one. I posted more details in another thread as copied above.