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Heater problem on 2005 Honda Pilot

I recently bought a 2005 Honda Pilot EX with 126K miles and automatic climate control. The problem I am having is that the heater does not get very hot, even on HI. When I run the heater, I can hear what sounds like trickling water under the dash when I accelerate. At this time the heater does get a little warmer. I am assuming this means that the heater core not blocked. I have no leaks in the cabin, although the Honda dealership recently told me I have a very small leak in the bottom of the radiator. The engine gets up to normal operating temperature quickly and stays just below halfway on the temperature gauge. Anyone have any suggestions? I would appreciate any help on this. I live in Maine, and it gets pretty cold up here!

If you hear trickling when accelerating, it means there’s air trapped in the cooling system.

Take the vehicle to a shop, and ask that they purge any air from the cooling system

That should get the heater working.

Tester

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It sounds like an air pocket is forming in the heater core possibly. Turn the heat on and top off the coolant in the radiator and expansion tank, engine running. See if that helps. If the heater core has air in it rather than coolant, could get cool air when the heater’s on. Ultimately, you need to repair all leaks in the coolant system in order to permanently fix it.

Your cooling system is low, refill it and the air in your heater lines will no longer be a problem.

If you have even a very small leak in your radiator, makes sense to replace it. Radiators aren’t generally overly expensive to replace, and if you have a leak the cooling system isn’t able to hold pressure like it should, so you are risking one day experiencing an engine damaging overheating event… I concur w/the guidance above, the heater problem is most likely air in the cooling system.