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Lack of heat

I have a 2008 Honda CRV. I have been having an ongoing problem with lack of heat. This started about three months ago. My mechanic replaced the thermostat (twice) we thought we might have gotten a defective one. We flushed the radiator and heater core forward and backward and under pressure. Still very little improvement. Took the car to local dealer who advised that the radiator and heater core needed to be replaced. Had my mechanic replace the radiator for far less than the dealer. No improvement. We cut open the old radiator and could find no sign of corrosion or obstruction that would restrict the flow of coolant through the system. It does not seem logical that if there is no restriction in the radiator there shouldn’t be any in the heater core. The dealer had advised that it appeared that the blend doors and controls seemed to be operating properly, although what little heat we were getting was not consistent through all dash vents. There was a noticeable difference between the drivers side (colder) and the passenger side. We decided to replace the water pump. some slight improvement but not much. Noticed that it seemed as though the coolant fans behind the radiator seemed to come on more than necessary. I pulled the fuses for these fans and drove the car for nearly a half an hour with no change in engine temp and no improvement in heat. I am well aware of the monumental task to replace the heater core and the potential for other things to go wrong as a result. The car has over 130,000 miles. Last option would be to look for replacement and move up a couple of years.

Does anyone believe this is definitely a problem with the heater core or does anyone have any other ideas either from experience or any anecdotal information. At this point I am supplementing the heat with two 12 volt electric heaters.

Any info or suggestions would be greatly appreciated

I am not sure how your car works, but 2 optons come to mind. Some cars have a control that allows warm fluid to go to the heater core, then there is “There was a noticeable difference between the drivers side (colder) and the passenger side” and that is an indicator to me of blend door problems.

There is really no need to guess about the heater core. I’m actually surprised that the radiator was replaced on something of a guess. The heater core has two hoses going to it. One is an inlet where the hot coolant flows in. The other is an outlet where it flows back out. The temperature of the hoses can be so easily measured that you can even use your hand. If you leave the blower fan off, and the car is up to temperature then both hoses should get hot. If the blower fan is cranked up the inlet might be slightly hotter, but you’d probably need a thermometer to find out.

In any case - find your heater hoses. Get the car up to temperature. Make sure the temp controls inside are set to heat and feel the heater hoses. Compare the feel of them to the upper radiator hose. (If you have an IR thermometer just use that).

Are both heater hoses hot? Are they somewhat similar in hotness to the upper radiator hose? If yes, then the problem is in your interior duct work - probably the blend door. If no, then your heater core is clogged - except you sort of already know its not since it was flushed. OR - through all of this, no one has yet to get all of the air bled out of the cooling system. Ask about what has been done to check for trapped air in the heater core.

Unfortunately, fixing the blend door is sometime almost as much “fun” as replacing the heater core.


Important questions . . .

You said you had poor heat, but do you also have poor airflow from the panel registers?

I too thought of the flow valve. Typically you’ll find that on the firewall, Follow the heater hose.
You can check that by simply turning the heat on high with the engine fully warmed up. Both the hose going into the valve and the one coming out should be hot. If one is not, I’d remove the valve and bench test it. You can activate the solenoid using two 6VDC lantern batteries connected in series.

If both hoses are hot, than since the heater core has been replaced your possibilities are bad blend door operation or perhaps a bad fan not pushing a sufficient amount of air. Again, that can be bench tested with the 6VDC batteries. Actually, I’ve tested one before with a 9V transistor radio battery.

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