A8bil

So you know those two black cylinder things on the drivers side of the engine compartment, just inboard of the brake fluid resevoir? My starting screeching badly and I can feel pulsing of the fluid in the bleed hoses that go into the firewall just in front of them. So, my question is, what do those two cylindrical pieces do? Can I just unhook them without adverse consequences? And, why in the heck did they start screeching out of the blue? My coolant got a little low a couple weeks back. Is it possible they need to be primed or?


Thanks in advance.

Bill

PaulW

<img src="http://www.audipages.com/images/hvac1.JPG">

I can't remember without looking it up....but either they are both throttle valves for the heater core (left and right side) or one is a throttle valve and the other is the after run pump.....which is normally energized when the car is running. The after run pumps die after a while and make the noise you describe.

Unplugged the connector shown (verify wire colors) and the afterrun pump won't work any longer....but your noise should stop, and you'll still have heat.

brittcrowell

I took this video with my digital camera a few weeks ago with the intension to post the same question. Here is the video, the ignition was switched on but the engine was not running, the sound is coming from the pumps only.<ul><li><a href="http://www.brittcrowell.com/2008/A8pumps.MPG">http://www.brittcrowell.com/2008/A8pumps.MPG</a</li></ul>

A8bil

Yep, those are exactly them and mine are making the same noise. Any problem with having them disconnected?

Thanks in advance Bill

kupplung

If they make alot of noise it could mean your cooling system isn't bled properly. Check the Bentley, remember reading it recently and will be there soon.

PaulW

Yea....but I've disconnected at least 3 over the years. Almost sure it's the pump

PaulW

No problem disconnecting the pump, it just won't circulate coolant in "REST" mode

MrMoneyPenny

I am getting this noise. Recently had the oil cooler pipe replaced and the coolant drained and replaced, which might have caused this problem.

Apart from disconnecting the wire and disabling the pump, how do I fix it, bleed the air so that it does not make that awful noise anymore?

Is it a question of re-flushing the coolant, empty and refill?

Or, is there a way to re-prime the pump?

Thanks
2001 Audi S8 (d2)

silverd2

If you're lucky, the system just needs bleeding correctly, with the bleeder valves on top of the heater hoses on the engine side of the firewall.

The system WAS filled with nothing but G-12 (pink or red coolant), right?

MrMoneyPenny

Afraid the last mechanic, after the oil cooler broken pipe replacement job, filled it with Green Coolant just last month.

Will have it replaced with W12 (red / pink) stuff shortly.

Hope that does not create an issue.

I tried to clear the air via DIY procedure, warm the car, run the heater, open the coolant expansion tank cap, some air came out and the noise would dissapear intermittently but would come back.

Will do a complete coolant flush and refill.

Any other suggestions?