LOW HEAT

[Никита]

Greetings!
Car:
2003 Honda Accord EX V6 Coupe. (A.T.)

Problem:
When it gets colder out, the heater will not produce any heat on startup when the engine is cold to the point when you cannot defrost an icy windshield. Only when driving on a highway it gets to acceptable hot temperature. Once you stop on a light or simply slow down, it will blow about 70 degrees at max. That only happens when the outside temperature gets to approximately 40-45 degrees and lower.

What I have checked/done to find the problem:
1. Purged air out of the system + added “Honda Type 2” coolant following the service manual procedure.
2. Visually checked the coolant state, check coolant voltage (higher voltage suggest high acidity), used hydrometer to check up to what temperature coolant is functional (hot and cold). Everything tells that coolant is okay.
3. Checked if the heater core valve opens and closes when turning the switch cold/hot.
4. Checked the return hose coming from thermostat to radiator, it appears to be hot after a 20 miles drive meaning thermostat is working or at least stays open.
Sadly, with those steps, I could not identify the root of a problem.

What I think the problem might be:
1. The heater core valve appears to move back and forth on the outside; however, it could possibly be broken on the inside and would not open completely.
2. Thermostat would not close completely.
3. System could be clogged up (never seen it happening on Hondas though)
4. Possibly water pump went bad.

I am planning to replace heater core valve and thermostat together with complete coolant flush. Before I do that however, I want an advice from you guys about how could I identify the root of this problem?
Thanks for your help!

Topic

[college man]

I’m in the camp of the thermostat not working correct. 20 miles is a long time for this car
to come up to temp. Replace the t-stat. flush the heater core. when you flush the heater
core open and close the valve this will tell you if you get good flow in and out of the core.
also if flow stops when closing the valve the valve is doing its job. no need to buy a new one.
more in this link.

http://www.ericthecarguy.com/faq/what-to-do-when-your-engine-overheats

[Ben Schwald]

I agree, that it is most likely a thermostat stuck open. It’s super easy to take out and check. When replacing I recommend the genuine Honda part. it’s not that much more expensive.

[Никита]

Thanks for your suggestions. One thing at a time makes more sense. I’ll will do the thermostat and heater core flush first and then let you know if that fixed the problem.

[Author]

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