My '04 EX has 125K miles on it. Lately I have not had heat at idle. I saw the previous thread here about coolant levels, so I made sure it was full. Didn't fix it, so I had the coolant changed. Still no fix, found a TSB about air pockets in the coolant lines. Followed the TSB to run it through two complete fan cycles with a funnel on the radiator filled with coolant. Still not fixed. Then I had the timing belt/water pump etc changed, which changed the coolant again, but it still isn't right.

Engine temperature appears to be normal, and the heat is good once the rpms are up, but as it sits at idle, if you put your hand on the lower radiator hose, its cold. If it sits til the fan comes on, the lower hose will get hot and the heat will blow hot, but as soon as the fan is off, the hose gets cold and the air blows cold again.

What do I try next? Thanks.

 

Is the engine warming up and staying warmed up? If temperature gauge doesn't stay at the middle, thermostat is stuck open.

Could also be a restriction in the heater core, you could try flushing it. That is best done by draining the system, disconnecting the core and forcing water through it backwards with a garden hose.

 

The engine is warming up and the needle is staying where it should be, which makes it appear that the thermostat is functioning properly.

What could cause a restriction in the heater core?