Dilemma: 04 A6 2.7T (45k miles) blows cold air through the front defroster when the car is stopped.

When the car is in motion it blows hot air. It has been 0 degrees to -25 for the last week.

Any help would be appreciated

 

A friend of mine had that exact same problem on an 1998 Mitsubishi Diamante. He had a hole in a hose leading to his radiator (not sure which one). When he repolaced this hose everything worked fine. Don't ask how or why it worked, but thats all he replaced and everything went back to normal. Hopefully someone can offer a little more insight.

 

Coop,

I have the same problem with my 97 A6. I maintain that it is a water pump problem, worn impeller. It won't pump enough at idle to push coolant through the heater core.

Wish to heck either me or my mechs had though to replace that and the Tstat when they replaced my engine. I'm told it is the equivalent of a TB change to do the pump and Tstat.

At longish stoplights, I put it in N and rev the engine to 1500 or so to get some water flow.

? Have you ever let it idle for 10 minutes or so, and had it overheat, blow the pressure cap? The 2 times I did that, it boiled over without the fan coming on. I THINK, but do no know, that there is a thermo switch in the rad to run the fan.

Good luck on any remedy you find.

Cheers,

George

 

Sorry guys i think u both need heater core ther is one way to find out between the battery and the brake booster u have both heater core hoses toutch them in idle engine hot and see if one is cold and the other is hot if it is that meens there is no circulation

 

Thanx guys,

I'll check the hoses then the H20 pump and T-stat. Unfortunately it has been 0 to -25 degrees so the car doesn't seem to overheat and I don't want to risk it. Never want to overheat a turbo car.

Like I said the heater works great while moving but not stopped, then it's ice cold. The pump idea sounds like the ticket. Was going to change the timing belt soon anyways just to be safe. Friend TT blew its belt at 50k and destroyed the motor. Figured it was a little early (45k) but better safe than sorry.

Anyone recommend a parts dealer to buy from? I use Pelican for my 325ix.

 

I have a 2002 Passat V6 with the same problem (basically same engine), but it has a new water pump. I have bled the air out at the heater core following the Bentley instructions but it seems to lack flow from the engine to the heater core????

I have flushed the heater core forwards and backwards and it flows with very little restriction. I doubt that you have a bad water pump because the impellers simply don't wear out - they fail outright when they fall off or break off the shaft.

Sorry I'm not much help - just remember to post your fix if you get it figured out!

 

Getty,

Mine's a 97, no battery located there. Did some steal it? (Nah, it's under the rear seat.)

My heater core was flushed when they pulled the engine to replace it. Still had NO heat. Went to my Foreign car boneyard, good mech, there, put a vac pump on the heater valve and, I think, broke it loose. Got it to start working. From that point, when engine is over 1500 RPM, have heat, and engine does not over heat. At idle, it will overheat in 5 to 10 minutes, and even with steam and 21 buck a gallon coolant pouring out, it throws no heat.

I say the pump is not moving coolant, at least in my case. The only other posibility I can see would be a vac leak in that line that will not open the heater valve at idle, but that would not account for the overheating.

Loach,

I have read elsewhere, maybe on this board, that the plastic impeller model WILL wear away. Or break and fall off, or however they fail. Since mine is not out, I don't know my problem, or if I have a plastic or metal impeller.

On a side note, the garage I hang out at (crippled up some, I don't do much, so loaf up there), mech asked me why a car they had in blew warm air when the revs were up, but cold air at idle? They had changed the Tstat. I said it was the pump. They thought not. Next day, went back, asked about it, they said it was the pump, all kinds of heat at idle.

Oh, yeah, for LOACH (caps to catch your eye) try operating your heater valve with a vac pump and see if it moves. Yours might be shot or it may be stuck. Work it a few times and try the heater. Try a vac gauge on the line to it and see if you get a signal, too. CC control head may have a fault, no vac to the valve.

Good luck to all of you.

Cheers,

George

 

George,

Thanks for the suggestions. Unfortunately I don't think these cars have a heater valve - they have flaps for the air only. I have checked my climatronic unit with VAG-COM and have no problems with flap positioning. Argghhh!

 

OK Guys, just to get this right......

Little to no flow through the heater core at idle= no heat in car at idle

With rpm's flow increases through core= awesome heat within the car

So my dilemma..... Water temps stay perfect (which on a turbo car are hard to do unless the cooling system is working perfectly) even in below 0* F temps.

So what control item (in the heater line path) can control the coolant at idle and allow it to flow during rpm's? If it is the impeller will/can it flow enough during rev's but flow very little during idle?

If it is not the pump, what else can it be? The way I understand it, either the heater core is blocked or it isn't, no in between. A vacuum leak may explain it but where do I start looking first?

Thanks again guys!!!

 

Loach1,

Unless they did away with the valve between your 2002 and my 1997, they most assuredly do have a valve in the inlet to the core. Mine have had them back to my original 1980 5000 Diesel.

It is under the plastic cover behind the firewall, about dead center of the car side to side. Mech at the boneyard pulled the hose, attached the vac pump and said it was working, possibly GOT it working with that pump, but still no heat when he reconnected, but it was at idle, so it either had not enough vacuum at idle, or no flow at idle because the pump is not pushing water.

Mind, I had no heat at any time before he applied the vacuum to it, did after, and still do, but not after 30 seconds or so at a stop light or whatever. I think the time is because it has rarely gotten below the 20's here, and the OP is talking about near zero. He might be blowing ice cold after 10 seconds.

Ah, well, I have to get this fixed soon, I'll let you know if change out of pump-Tstat helped.

Cheers,

George