4.2 TDI engine noise

[vajper]

Tried to pull the front belt yesterday to see if the sound came from the alternator/compressor/pulleys without success. Even though I could get a spanner into the 3/8" slot on the tensioner it was a lie to move it. You would need really small hands to slack that belt to pry it off the alternator...

[vajper]

Had my old trusty mechanic to have a look at the car today. He was pretty confident the alternator was the source of the sound. He also noticed that the belt tensioner was in bad shape. Might even be that the tensioner is the source of the sound. Didn't ask him if he had the belt off because of the tensioner.

He had some troubles sourcing a refurbished alternator + tensioner but I guess that was due to not having the correct part numbers. Normally he doesn't treat V8's that often

Can someone confirm that the alternator part number is 07 903 015Q and the tensioner 057 903 133J?

I'll see what I will do, maybe I do the job myself depending on what he offers. Looked at the repair guide and it seemed doable in a normal hobby garage without lift.

Can anyone tell if I need the special vacuum tools for refilling/bleeding the coolant system after the job?

[steamship]

Correct part number for the alternator is 059903015PX. The tensioner number you have is correct.

As an aside, it's a good idea to update your signature to include some specifics about your car. That makes it easier for others to identify which specific model you're referring to, although in your case you did mention this in the first post - '2005 A8 D3 4.2 TDI (BVN)'

[vajper]

Thanks for the confirmation!

I ordered a third-party (not refurbished/rebuilt) 059 903 015P. Let's see how that ends. With some luck it is not the alternator but some of the rollers/tensioner but in that case the alternator goes back to the supplier.

Also remember that I have some small leak on the coolant system, will need to locate and fix that at the same time. Hopefully it ends well, a long time since I spent time in the engine compartment on my car. Promise to document with some pics!

[vajper]

Yesterday I got it confirmed that the alternator is broken. Even though the voltage reads OK when engine is on (14+V), the battery isn't charging properly. Became obvious when all electronics started failing during drive, ending with the gear box putting itself in neutral

Quite impressed the battery stood up that long. Let's hope I get the spare parts before Christmas.

[vajper]

Tried to locate the coolant leak today. Spent several hours trying to locate one single drop of coolant anywhere. Without success Let's hope it doesn't end up in the oil... (didn't look like that last oil change at least).

Any advice on common leak places? I raised the pressure in the coolant container to 1bar and couldn't locate one single drop over several hours even though the pressure slowly released. Won't be able to refill the system using vacuum after alternator change with this leak. Damn car

[vajper]

OK, you gave me your time. I give you a follow-up and some pictures

So, the alternator gave up and I ordered a new alternater + a belt tensioner that I suspected to be bad. Unfortunately I missed to order the two gaskets for connecting the cooling to the alternator. Wasn't worth chancing re-using the old ones. Christmas Hollidays messed up the delivery so first chance to take on the job was this week.

I don't have that much experience working with cars but this kind of job is more of a tear-down-replace-rebuild job. I have removed the front wheel house liners + front bumper a couple of times but not more than that.

Started the job before Christmas by printing the necessary guides from ElsaWin. They are pretty OK but the main problem with all these guides is that you sometimes have no clue where a part is situated. Even with a detailed figure it is impossible to locate the area.

I used one evening to prepare for the work and to do as much as possible up until removing the lock carrier which required a few more hands than I possess.

Yesterday I started from that point. Everything took it's time but no major problems or stuck screws. Had to be creative to remove one of the screws on the motor torque support (welding a handle to a allen wrench). Also I found that some steps in the guide was easier to carry out in a different order.

With the front off, I got confirmation on the broken belt tensioner. Corrosion had cracked the spring mount. After removing the belt, the source of the noise was obvious. The alternator was really hard to rotate, bearings probably worn out.

I replaced it with a new third-party one (yeah, don't plan to own this car forever). The swap and the following re-build of everything was actually really pleasant.

The re-build wasn't made in the exact reverse order because I wanted to get the coolant system together to find any leaks early. Used a chineese kit for vacuum refilling. That was a first time, worked out really well. Then put the system under pressure for the rest of the work time to ensure no leaks.

When everything related to the engine was in place I started her up and ran through the recommended steps for bleeding the coolant system. Engine sound was back to normal and alternator was charging as it should according to VCDS.

Finally put the bumper + wheel house liners back and then cleared all fault codes caused by battery disconnection. Took her for a 15 minutes ride and again checked for fault codes. Seems fine. Really fine. Me happy

A few thoughts:

- Is there any good way to locate different things in the car? I mean, it took me 10-15 minutes to locate the darn front airbag sensors event though I knew they would be somewhere in the lock carrier.

- A bit strange that the alternator failed both in bearings and in charging functionality (diodes?) at around the same time.

Five pictures from yesterday:


Lock carrier removed


Closer view


Alternator removed, note the belt tensioner


The darn thing removed.


New alternator, belt tensioner and belt in place

Thanks for answering my questions. Let's see what's up next