View Full Version : Heater core question

10-08-2010, 07:16 AM
So my heating isn't blowing as hot as it use to anymore unless I turn it up to max temp like 29 C degrees. Last weekend I flushed the core and the coolant was very clean and the water flow coming out was pretty good so didn't seem like anything was blocked. The thermostat and coolant were replaced last winter and the car is heating up in normal amount of time and staying at 90C degrees regardless of highway or city driving. My mechanic recommended I fill the core wih CLR and let it sit for a bit and flush it again. Any other suggestion anyone could recommend? I just don't want to have to flush it for the 3rd time. Heater core is not leaking as i don't smell any coolant through the vent. I don't think there's any air in the system as i've driven the car about 600km since the flush so it should be good by now and i only flushed the heater core not the entire engine.

10-08-2010, 11:56 AM
Anyone? walkytalky?

10-08-2010, 04:46 PM
First thing to do is check for codes using the on-board HVAC diagnostics. Make sure there are no mix flap codes, etc.

Can you explain how the heat is operating? Is it hot, then gets cooler after a bit? Does it work good when driving, but lousy when idling? Does raising the revs to 3k at idle make any difference?

CLR isn't a bad idea. I've used Dran-o before, but that is pretty extreme. I'd probably try CLR the next time I have to flush the core.

If you don't have any codes and it just seems like the cool/hot air mix is just out of calibration, you might want to take a closer look at the HVAC sensor outputs. See what it is reading for cabin temp, outside temp, plenum temp, vent temp, sunlight detector, etc. You might find something that is reading lousy, but isn't setting a code. I know for a fact that the outside air temp has a lot to do with the heat mix flap position.

10-08-2010, 05:23 PM
Thanx for all the info. I have a vag but don't know how to read all those things unless i know exactly what measure block i should read. The heat does start off pretty warm but just turn cold after a while. I'd say around twenty minutes or so after the car is started. It gets hotter if i turn the temp up. The interior still warms up enough but it hasn't gotten properly cold up here yet and i don't want to find out the hard way in the middle of winter that the heating is not blowing hot enough.

10-08-2010, 05:38 PM
You don't need vag-com for this, you can just use the on-board HVAC diagnostics.