TDI Blowby: Causes & Solutions for ALH Engine

Hello!

Here's a brief introduction about me: My name is Stephen, I am 22 years old, and I come from Hildesheim, near Hanover. I have been reading this forum for quite some time, have received many helpful tips here, and even purchased my VCDS here. I have been working on cars for a while now, and I've generally been able to solve problems well. However, in this case, I'm at the end of my rope .

Subject: My Golf 4, 1.9 TDI, Engine Code: ALH, 313,000 km on the clock, is leaking oil like crazy from the oil filler neck. I have already replaced the oil cap including the gasket twice, and the ventilation valve on top of the valve cover. I also measured the compression in the cylinders through the injectors -> all are within the normal range and consistent. My engine is constantly covered in oil, and you can clearly feel the air being pushed out of the oil filler neck when the engine is running and the cap is open... I'm not really sure what to do next.
Can blow-by also be caused by a damaged turbocharger shaft? While I couldn't detect any noticeable play there, I don't have the experience to know exactly how that would feel, and the turbocharger has already accumulated 270,000 kilometers.
Could it be related to my retrofitted DPF? Perhaps the exhaust gases can't flow as well and are escaping from there?
I am truly grateful for any advice you can offer.

Best regards,
Stephen

Hello Stephen,

If the engine is idling and you open the oil filler cap, leaving it loose, will it immediately fly off, or will it stay somewhat in place, wobbling slightly?

Given the mileage, a crack in the piston is possible, but that should be evident during a compression test.

Is the oil level correct? How much oil was added? For an ALH engine, approximately 4.5 liters would be a good starting point (but this is not an exact value).

Is the crankcase ventilation system (the round black plastic plate with the hose connection on the valve cover) working properly and not leaking oil in the area?
The round plastic part is prone to breaking.

Best regards, Rainer.

Hi Rainer,

Thank you for your reply. When I put the lid on, it bounces quite a bit and then sometimes falls off after 10-20 seconds.

There is no oil surrounding the gearbox; it has also been replaced recently.

The oil level is correct. However, I've had to top it up occasionally because some of it has been leaking out through the cap.

Perhaps I won't be able to avoid having to take the head off .

Greetings.

Quote:

Maybe I won't be able to avoid having to take my head off at some point.

Perhaps you should try a new oil filler cap first. It should remain sealed as long as the ventilation system for the crankcase is working properly.

What are the compression values? Is the hose from the EGR valve to the intake air duct clear and unobstructed? Is the intake manifold free of obstructions?
Is the leak only coming from the oil cap?
The turbocharger and cylinder head should not be considered as potential causes.
hg
Herbert.

Thank you for your help!

Autoservice wrote:

Quote: Maybe I won't be able to avoid having to take my head off at some point. Perhaps you should try a new oil cap first... it should remain sealed as long as the ventilation system for the engine compartment is working.

The lid arrived new, but unfortunately, it stopped working again after a short time .

It seems like there's still a leak at the EGR valve. Could it be that the valve is sealing tightly, causing air to escape through the cap because it can't pass through the ventilation system? But if that were the case, wouldn't the engine generally have trouble getting enough air and experience power loss? I don't actually feel any of that.

The turbocharger's intercooler connections are also slightly oily.

I will measure the compression again and list the exact values here.

Thank you very much in advance!

Best regards, Stephen.