I have 1997 Civic DX hatch manual trans. D16Y7. I have installed a new thermostat, radiator, and water pump and still can't get sufficient heat out of the vents. I have checked everything that i know to check, both heater hoses are hot coming to and from the heater core, the heater control valve is open, I have good coolant flow through the radiator, but still the air coming out the vents is barely warm. Any ideas?

 

Check blower resistor.
Honda Part No.: 79330-SR3-A01

 

Flush the heater core. With both hoses disconnected from the engine, you should be able to send the full flow of a garden hose through the core with little resistance.

Make sure no air in the cooling system, follow the air bleeding procedure.

Check the air door. When you move the lever from cold to hot, a big door inside the heater box either diverts air around the heater core or sends it through. This is controlled by the mechanism on the bottom of the box. If you don't have A/C you can remove the air duct behind the glove compartment, between the fan and heater box and watch the door move. If you do have A/C you'd have to remove the evaporator box, which requires recovering the refrigerant.

 

last time i bled coolant system it did not go well.
finally bought the fancy funnel and it did help so worth it imho:


cheaper on ebay if you dont have prime.