Crankcase Ventilation: Blue Smoke & 2.5 AFB Engine

Hello everyone,
"I've been experiencing issues with burnt oil in the exhaust for the last 500 km on my 2.5L AFB engine (110 kW, manufactured in October 1998, 147,000 km). I replaced the turbocharger with a brand new one 300 km ago and cleaned the entire turbocharging system. However, the blue smoke from the exhaust is still present. I suspect that the crankcase ventilation system may not be functioning correctly. When I open the oil filler cap with the engine running, I hear a noticeable hiss and see oil mist escaping, indicating excessive pressure in the engine. I've now disconnected the crankcase ventilation system from the intake manifold and blocked it with clean cloths. As a result, no oil is entering the intake manifold from the crankcase ventilation system. Could it be that the relatively high pressure in the crankcase during the "intake stroke" is forcing oil past the oil scraper ring and into the combustion chamber? At what pressure should the pressure relief valve open on the AFB engine? Is a pressure of 0.5-1 bar in the crankcase normal? Can the pressure relief valve be replaced individually?"Thank you for your contributions!

Hi,
I can't imagine that a significant amount of back pressure is normal or desirable. In particular, the various shaft seals are usually not designed to handle such pressure.
In my engine, there's even so much vacuum that, when idling, no gases escape through the open oil filler neck.
Show it to an experienced mechanic or someone who knows about engines and see what they say about the results you're getting. If the amount is unusually high, that could be an indication of a serious problem (severe wear or a faulty piston ring).

Yes, the suspicion arises - a piston ring or something like that - but I actually have another theory, and I've also already posted about the component in the forum, e.g. https://community.dieselschrauber.org/en/viewtopic.php?t=1271&highlight=%F6lverbrauch.
"I've found it. I've now removed the entire oil filter module (which was a messy job) and I've determined that the overpressure likely originates from the pre-filter that's supposed to remove contaminants from the "air." This pre-filter operates under pressure. Perhaps this component has other problems besides the leaf spring issue described in the link."

If you don't have the means to do it yourself, have the crankcase pressure measured. It only takes a few minutes. To do this, the measuring device is simply attached to the oil dipstick tube. The pressure must not be higher than 5 mbar; otherwise, the oil mist separator must be replaced. However, excessive pressure is usually also noticeable by slight oil leakage at the cylinder head covers.

Best regards,

Hello,

According to the manufacturer's specifications for the first 2.5 V6 engines, the crankcase pressure should be checked every 60,000 km. The reason for this was apparently a design flaw in the filters that caused them to become clogged with oil sludge. Because my A4 2.5, manufactured in 2/98, was losing oil, I suspected the filters. Unfortunately, replacing them didn't change anything. In addition, the entire intake system was full of oil, which is why I disabled the EGR valve. However, my main concern is the turbocharger. After all, you can't expect a turbocharger in a product like Audi to last more than 110,000 km under normal driving conditions, can you?

Thank you very much.
You're encouraging me.
The loader is already new, and the oil isn't coming from the intake manifold. But that filter was quite clogged.
Let's see what comes out of this. I'll keep you updated.

@der_marco

Hi, has your problem been resolved yet? I'm experiencing the exact same issue. My mechanic wants to replace the entire engine, which will cost over 10,000 euros. There has to be another way.
I also have an AFB (American Federation of Boise) membership from 8/99.

Sure, here is the translation of the text from German to English:

'Hello'

v6Motion

How many miles are on your engine now?

Here's a private message from Marco, by the way.


'Thanks for the tip.'
It was a bullseye.
The oil separator was completely sealed.
However, this was the first time it happened since I started driving the car, which has about 80,000 kilometers on it.
Do I need to start including the cost of oil separators more often in my calculations?
Thank you again!

freundl. Greetings.

Marco

As far as I know, this issue is common with AFB systems, so please have your case pressure checked.

Best regards,

@ Marco:

How much goodwill did you show us? Hopefully, you installed the improved part from AKN.

Best regards,

@vikinger

KM: 91000

'I had the same problem 2000 km ago. At that time, it was said that the crankcase ventilation system was sealed. It was then fixed, but now I'm experiencing the same problem again: the pressure in the crankcase is 270 mbar.'
Compression pressure in all six cylinders below 19 bar.
They are now installing the oil separator from the 132kW model. Let's see if it works then. The engine has been tuned with a Cartronic Powerbox - that's why VW is not offering any goodwill, and a special request for goodwill was also denied.
A cost estimate of €10,100.00 is available.

Are there any other ideas, or should I get it repaired and sell it quickly?

Hi.

v6Motion

Did you happen to adjust the valves for some reason, perhaps after a timing belt failure? If so, a piston ring might have become stuck.
Is it possible to purchase the oil mist separator separately now? As far as I know, the entire oil filter assembly used to have to be replaced. How much does this whole process cost?

@vikinger

I'm not aware of any timing belt issues – since I've owned the car, there hasn't been any problem with it.
Regarding the cost, all I know is that the part is from Audi, as it's supposedly not available from VW, and it's supposed to cost €120.00.

Do you know any more details or a part number?

Yes, exactly... that's the right price range. Then the entire oil filter module will be replaced again (the filter holder with valve, etc., should be part number ET 059 115 405 D, guaranteed). However, that doesn't include the installation time, which is quite significant (the crossmember needs to be lowered, the pump needs to be removed, the turbo needs to be removed, etc.). Well... driving an Audi or a VW is definitely an expensive hobby (or maybe more of an expensive frustration ).

Best regards,

@Vikinger

Okay, great - I've already paid 238.00€, including the compression test. Regardless, I'm probably going to have a leak test done so it's clear which piston is leaking where.

If the pistons are actually damaged, a new engine will be needed.
Do you have any idea if I can install the AKE (132kW) without major modifications?
The engine control unit is available, and I can also get the entire engine – including the turbocharger, fuel injection system, etc.

Do you have experience with that, or would you prefer an AFB or AKN instead?

Sure, here is the translation of the text from German to English:

'Hello,'
v6Motion

As far as I know, the main difference lies in a different pump and different nozzles. I would definitely consider such a conversion to be within the realm of possibility.
Considering that my engine now has 70,000 kilometers on it, it's also just over three years old, and therefore any discussions about warranty coverage are likely over, I'm starting to feel anxious.