I've been having issues with my heating.
when on and full, it blows cold after warm up at low rpm. when running at 3000rpm it goes hot, but not as hot as it should.
I did a rad flush and changed the Thermostat. I ran it to remove the air from the system.
The thing is, that did not remedy the problem.
Now I have read the forum and get confused *** to the replies.
Like most forums, everyone is an expert.
I'm looking for definitive advise as to where I should go from here.
I am no stranger to Engines and how they should work.
Some of the answers I have seen on the forum regarding this problem are daunting.
It ranges to;
1. Heater core
2. Head Gasket
3. Heater control valve.
Now looking at No 1. I have not investigated this problem as yet.
No. 2 surely it would be noticeable if the head gasket would have gone?
You would notice a lack of power in the engine and oil in the water system or water in the oil?
The heater control valve is opening and closing as it should.
So is there any one on this forum who could give me a straight answer to the problem.
Preferably a Honda Engineer who has seen and dealt with this problem?

 

I'm not a Honda engineer, but I've been working on & building them for 21 years.

If your certain there is no air in the system then I would check the flow through the core. It sounds like your heater core is partially obstructed. The cheap solution would be to back flush the heater core.

I do this by disconnecting both inlet and outlet heater hoses, fill the outlet side with water then hook up an air compressor to the outlet side. Give it the max PSI your compressor will handle. Then use a water hose and flush it with clean water. Do it a couple times.

If you can't establish good flow on both sides with a garden hose attached (output = input) then the core needs replacing.

Good luck