APU 1.8T Dump valve noise???

[Foilpact]

Hi there, Ive had my Passat for over a year now without a problem but recently it has started to make a dump valve noise...

It can be heard louder when i drive hard and lift off quick. The noise has slowly got louder over the last week..


Also, are the turbo's on these cars usually quite loud... Well not loud but u can hear it quite clearly when it comes onto boost? Ive been in a few other turbo cars and their turbo's could barely be heard. Even on a new Astra Sri 200 the turbo can only be heard if u've got the window down and push it hard...

ne way thx for the look, Foil

[Ross 1.8T]

Hi there, Ive had my Passat for over a year now without a problem but recently it has started to make a dump valve noise...

It can be heard louder when i drive hard and lift off quick. The noise has slowly got louder over the last week..


Also, are the turbo's on these cars usually quite loud... Well not loud but u can hear it quite clearly when it comes onto boost? Ive been in a few other turbo cars and their turbo's could barely be heard. Even on a new Astra Sri 200 the turbo can only be heard if u've got the window down and push it hard...

ne way thx for the look, Foil

If its making a "chattering" dump noise, your dump valve is knackered and is not venting properly causing pressurised boost air to travel back over the turbine blades creating the chattering noise. A symptom of compressor stall. Replace your valve soonest.

Turbos on the 1.8T can be very noisy. Nothing to worry about unless you have blue smoke from the exhaust.

[Foilpact]

Cool, thx.

Where is the dump valve located about and how much will it cost roughly to replace?..

Also, is there any way to check the condition of the valve? I assume its the N75 valve that ur on about?...

[Ross 1.8T]

Cool, thx.

Where is the dump valve located about and how much will it cost roughly to replace?..

Also, is there any way to check the condition of the valve? I assume its the N75 valve that ur on about?...

No its not the N75. The N75 is VAG speak for a Boost Pressure Control valve.

The diverter (dump) valve is located at the front of the engine bay. Remove the plastic engine top cover and you'll see it. Its a matt black cylinder with a small vacuum hose on the top and larger connections to the turbo->intercooler and airbox->turbo hoses.

You can test it by doing the following:

1. Remove it from its location in the 3 hoses. You'll need 2 jubilee clips and a cable tie to replace it, as Volkswagen use one use clamps to install them in the factory.

2. Look in the bottom port of the valve and you'll see the grey plastic diaphragm. Push it up with your finger and hold it there.

3. Place a finger over the small vacuum connection on the top of the valve and remove your finger from the diaphragm.

If the diaphragm stays in place, you can be 99% certain that the valve is ok as this demonstrates that its holding vacuum and therefore the diaphragm is not split.

If the diaphragm slips back down to its resting position. You need a new valve.

If you have the chattering sound when you lift off the throttle, you will definitely need a new dump valve. Do this sooner rather than latter as the noise you are hearing puts a lot of strain on the turbo compressor shaft.