It is starting to get down to the 30s here in the morning, and the last couple of days I have been having heating issues with my 06 A4.

The temperature gauge has never been erratic and always held a consistent temperature. I figured the problem was a clogged heater core, so I back flushed it, but didn't make any difference. The core wasn't plugged, nor did the hoses or inlets show any signs of gunk.

I did notice if the rpm's are pushed, it does it hot as it should. aka, either driving hard, or hold the rpm's at a steady 3k.

Also, I noticed after a drive (~20 minutes) the coolant inside of the core wasn't that hot. Within 5 minutes of shutting the car off, I pulled the top hose and it was warm, but not hot by any means--about the temperature when washing your hands. Also, there was a decent about on pressure on the top hose at that time too.

Here are the things I have tried/checked:

1.) Flushed the heater core. Seemed fine.
2.) Coolant level is fine.
3.) Tried bleeding any air from the system, however, I am not getting a constant flow of coolant through the heater core.
4.) I listened to make sure the flap valves were moving within the car.

Is there something that regulates flow into the heater core? It almost seems that there is something else restricting the flow into the heater core.

Side note, I did see a couple of other threads related, but didn't see anything that directly related to my issue....though, it is highly possible for me to of missed one.

 

How'd you purge the air from the system? There's a bleeder screw on the metal coolant line on top of the engine, don't lose the washer.

Open that and crimp the small rubber line running from the reservoir without damaging it.

Then squeeze the upper radiator hose, then place your finger(dont burn yourself with hot coolant) on that small breather hole and relieve pressure on the upper radiator hose. Do this until coolant gushes out that little breather hole.

I've done it so many times I forget the order of squeezing and letting go, it comes naturally so I may be off on the sequence. Either way you'll realize what you need to do and if coolant doesn't come spewing from that hole and all you hear is gurgling there's air in the system so you need to keep on. Don't worry you'll see the coolant gushing out sooner or later.

The upper radiator hose is the 2.5 in diameter hose right in front of right pocket, looking straight down on the engine. Can't miss it.

All this is if you still have air to purge.

All thermostats go, it's a matter of when not if with these cars. This will effect your heating.

 

I attempted the purge via the hole on the top heater core hose (as some else had mentioned). I will purge the way you mentioned tomorrow evening.

I figured if the tstat was going I would see erratic movement from the temperature gauge, but it has been steady, which made me think there was air in the system.

Thanks for the advice.

 

Forgot to mention the reason for crimping the small diameter tube coming out of the front of your coolant reservoir/expansion tank. It is because if you do have air your going to need to have the reservoir open to fill more g13 coolant and distilled water mix as the air is expelled.

The temp gauge would only go to a quarter of the way before my tstat totally stopped working. It was gradual till it eventually triggered an error code and finally the MIL. The heat wouldn't work correctly as well.