AFN Oil Leak: Causes and Solutions

Hello,

I have a slight oil leak on my AFN and I wanted to ask a question about it.

It could be either the seal or the hose that is causing the problem (see the picture).

It's difficult to define. I've already replaced the oil seal, but it's still happening.

There's still occasional oil leaking from under the vehicle.

'Leaks can be detected beneath this seal. The oil is likely leaking onto the...'

It flows into the oil pan and spreads out there.

The hose probably connects to the valve cover.

Is that the engine ventilation?

First of all: how do you access the area to replace the gasket and the piece of tubing?
I haven't even had a chance to wipe off the oil yet *g*.

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"In 95% of cases, it's the crankcase ventilation system. It tends to leak. When replacing it, it's a good idea to use a flexible joint. It's not ideal, but it's possible."

So, you mean it could be related to the tire, including the inner tube?

The oil filter housing next to it appears to be sealed, and everything seems tight from the top (i.e., above the vent).

With a mileage of 257,000 km, it's understandable that a seal or hose might occasionally leak.

As I said, 95% yes. I certainly won't give you a 100% guarantee if I haven't seen it live.

"I've experienced this problem with four 1Z engines before, and some of them had even fewer kilometers than yours."

Thank you!

'I had the same issue with the seal. Even after replacing it, it still didn't seal properly, so I used high-temperature silicone sealant to fix it. It was dry afterwards...'

Hello bonze,

'In my case, the flange of this hose, which is attached to the engine block, had cracked. Almost the entire engine bay on the left side of my A4 was covered in oil.'

That part cost around 28 euros back then (about 3-4 years ago).

To precisely locate the source of the leak, the engine compartment must be cleaned so that the leak can be identified after a test drive.
But this hose seems to be prone to failure quite often.

If you don't want to disassemble too much in the engine compartment, you need fairly flexible fingers/tools .

Have fun changing!

K.O.

Thank you very much, @oldewurtel.

I received this item today, and it cost €31.24.

I actually thought there would be a gasket on that flange, but it turns out there's only an O-ring.

I can also imagine that the plastic pipe on my flange may have cracked.

[Theory] - If I were to experience the same thing, I wouldn't attribute it to thermals, but rather to the rather rigid connection.

I'll take it apart tomorrow and post a picture of it.

Thank you again to everyone for your help!!

Okay.

Here's a picture of the removed hose.

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Everything went wonderfully, better than I expected.

As you can see, it's broken at the top of the fitting, and it seems to have become leaky at the bottom, which is evident from the oil.

The O-ring still looks good.

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Hello bonze,

Yes, that's exactly what my modified part looked like!

Okay, I found the errors...

Best regards,
K. O.

Hello,

Today, I replaced the crankcase ventilation system on my wife's Passat AFN (250,000 km) due to a leak – the flange looked exactly like the ones in the pictures.

Surprisingly, the engine had an oil separator installed, which, according to VAG documentation, wasn't used until 70,000 engines later. We've owned the car for a long time, and it was purchased from the original owner when it was only 2 years old – it didn't look like it had been installed later.

I wasn't in the mood for fiddling around, so I removed the oil filter, oil cooler, and filter housing, cleaned them, and then reinstalled everything with new seals, hoses, clamps, filters, an oil separator, and a pressure regulator. Let's see if it stays dry.