Piston Ring vs. Valve Stem Seal Wear

Hello everyone,
'For a while now, my car has been emitting a thick cloud of burnt oil smoke when starting up, even if it's only been sitting for a short time. However, the oil consumption hasn't noticeably increased; this issue doesn't occur while driving.'

From my perspective, the only possible causes are the piston rings/oil scraper rings or the valve stem seals.

What are the ways to differentiate these?


With gasoline engines, it's often said: warm up the engine, rev it up to a high RPM, then close the throttle. If it starts smoking afterwards, it's likely the valve stem seals. However, this test doesn't apply to the AFN engine.

Here's the translation:

'The thing that speaks against the piston rings is that I don't have a lot of blow-by. Also, in my case, the crankcase ventilation goes into a container, and there's almost nothing in it, which is different from what you usually see with engines that have faulty piston rings. My suspicion is that it's the valve stem seals, but maybe someone else knows a better way to diagnose it.'

Is there anything else anyone can think of that it might be? (It's not the turbo!)

Does anyone else have any other ideas about what it could be? (It's not the turbo!)

It could also be a nozzle that's dripping.

CU Gremlin.

or a hearty gulp of water from the cooling system?!?
The white smoke suggests the oil is not burning cleanly; in my experience, burnt oil usually produces a bluish smoke. Just take a quick sniff to check.

Marco wrote:

or a hearty gulp of water from the cooling system?!? What speaks against burnt oil is the white smoke; in my experience so far, burnt oil has always been bluish.

I agree completely.

To identify leaky piston rings, I still use the old-school method: Measure compression, remove the pressure gauge, pour a small amount of motor oil into the cylinder, and measure compression again.

The oil is supposed to flow (among other things) to the piston rings, help with sealing, and thus improve compression - if the rings are already weak.

If the compression value doesn't change, you can rule out the piston rings as the cause.


I'm not sure if this applies to TDI engines as well.

If all the oil only collects in the combustion chamber, nothing happens to the rings, but the compression still increases (depending on the amount of oil), if the gas volume of the small combustion chamber is "significantly" reduced -> a misdiagnosis seems possible.

@garth.brooks:

Are you sure the pump timing is correct? Check the injection start and inspect for any issues with the crankshaft pulley.

Regards,
Alex.

Hello everyone,

I checked it with my nose; it's definitely not water - it's oil!
The smoke is bluish-white, and there's no lack of water either.

@ Gremlin nozzle – that's another idea. Lately, it's also been producing soot even at full throttle, despite the 1.4 bar pressure. I had considered this to be unrelated and suspected one of my nozzles, but if diesel is washing oil out of the cylinder after being turned off, it actually makes sense.

Meine Düsen sind erst 2 Jahre / 40TKm alt. Ich mach die dieses WE mal raus. Let's see.

@ulf
I'm familiar with that trick of putting oil on the piston; it works well. I've used it on Otto engines before, but it doesn't work on TDIs because...
The waste runs into the combustion chamber hopper.
2. Consequently, the TDI engine may be prone to hydrolock or seizing. There's very little space left between the piston and the cylinder head, especially if the combustion chamber needs to be completely filled.

Gegen Kompressionsverlußt spricht der niedrige Blowby, wenn dann könnte ein Abstreifring hin sein, aber dann müsste er auch beim Fahren Öl brauchen. RicHow are you doing so far?

@donalexo Are you talking about the crankshaft pulley test? I thought that was only for the 1Z engine.
Fuel injection working properly, power is good. Engine starts perfectly.

Last fall, I had a small crack repaired on my wife's Passat/AFN.
The head gasket has been replaced. At the same time, I also changed the valve stem seals.
The parts were also replaced at the same time. The car had 155,000 kilometers (approximately 96,000 miles) on it and consumed oil.
approximately 0.05 L per 1,000 kilometers driven. The seals themselves were already quite hardened.
they probably would have started causing trouble soon. By the way, you can...
Valve stem seals can be replaced from above very easily - without removing the cylinder head.
to expand! I've been doing my own repairs and installations for over 30 years, and so far I have...
Very few cases of defective oil scraper rings - but many negative experiences.
with valve stem seals for Volkswagen and Audi!

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

'Hi Gremlin,'

This weekend, I was working on the nozzles, and nozzle number 2 had a small buildup of material around one of the holes.

So, I swapped out my 2-year-old car with 40,000 km on it for a 4-year-old one with 129,000 km, and sure enough, the excessive smoke during startup was gone.

If you happen to be around sometime, I'll give you one.