heat problem 2001 honda civic

2001 honda civic.

Pretty cold outside (close to -30C)

Car heats up (temp gauge) when not using fan (blower), as soon as I
turn the fan on, the temp gauge starts going down towards the C mark
and stays there.


I replaced thermostat (honda part) last year.

Is there anything else I could check?

Thanks.

 

How's the coolant level in the rad? Check when the rad is cool, not hot.

Is heater output poor?

 

How can I tell if the heater output is poor?

If you mean hot air coming out form the vents. Yes it is poor.

 

The air doesn't get as hot as it used to.

Did you check the fluid level in the rad and reservoir?

 

Yes, I checked and they are full.

 

Get the engine's heat level checked with an infradred thermometer. Any
garage will have one.

If the engine /is/ getting properly hot enough, you probably have either a
blocked dust filter in the blower intake, or the heater control valve isn't
opening properly.

When was the last time you replaced the dust filter?

 

Last year changed the cabin filters and the engine air filter.

It heats up pretty good till about -20C.

Thanks.

 

-20C? That's about -4F. Pretty cold. You might not actually have anything
wrong with the car. Heaters depend on engine heat for their operation. In
extreme cold, the heater will have trouble making proper output because the
coolant has trouble heating up in the first place.

However, it's the thermostat's job to close up in very cold conditions and
keep the heat in. That way the heater can take advantage of the trapped
heat. Chances are pretty good your thermostat is just getting old.

Replace the thermostat with new OEM, changing the coolant with new OEM at
the same time. That will at least make sure the heater will be able to make
the maximum amount of heat that it can.