How to stop MAF oil contamination (CLK 230K - W208)

[jamesmc]

It is believed that the info also applies to all W202 (C class) Kompressor engines.

History behind this.
There have been a few discussions in the Forum about MAF failure on the W208. This post covers the failure of the MAF - by oil contamination.

If your W208K has a mileage in excess of 90,00 miles
This is one job that you should carry out in the near future as a matter of preventive maintenance.
In excess of the above mileage even if your car is not suffering from this problem now it will, which is exactly why I did the job anyway.
The parts are cheap in comparison to replacing dead MAF sensors.
If you cannot do the job yourself approximately 4 hours labour should be allowed for a workshop to complete the job.

One Forum Member carried out a lot of research on the problem and, along the way, dispelled one particular myth quoted a few times in the past :

If your W208 (W202) has oil in the Air filter housing or any pipework leading, via the intercooler, to the MAF
then it will not be Kompressor (Supercharger) related failure causing the problem.​

The reason for this (as pointed out byjiminessex) is that, unlike a turbocharger, there is no oil feed from the engine to the Kompressor. The only oil the supercharger uses is held in a tiny inbuilt reservoir within the compressor body itself. This quantity of oil alone is insufficient to cause oil contamination to the point where it reach the MAF.


So, if it isn't a Kompressor (Supercharger) fault what causes the MAF oil contamination problem?
The research by jiminessex answers that:

The following applies specifically to my car, a 1999 CLK 230k Coupe with a 208347 chassis

no. and a 111975 engine, I believe the info applies to all 202 C class and 208 CLK class kompressor engines.
At 97,000 miles I became aware of oil in the air intake but it was then only a minor irritation, cleaning the MAF

sensor sorted it. By 140,000 miles the amount of oil in the pipework to the MAF sensor was becoming alarming

although it only caused a misfire and was solved again by cleaning.
Examination of the air filter housing showed the oil was entering the system from the Crankcase Breather System.

My understanding of the Crankcase Breather System:-
It operates in two modes, an upper partload to full load system and an idle to upper partload system.

The idle to upper partload system works directly off the crankcase and feeds into the cylinder head just before the inlet valves. The high load system from the cylinder head cover feeds into the air filter housing AFTER the the filter element.

The highload system is mounted on the cylinder head cover and consists of a black plastic oil separator and three hoses,it is very accessible and cheap to replace all components. Beware, get the parts first as the hoses are brittle with age and at least one will probably break. Changing all this did not solve my problem although it was clear that the oil was coming from here!

Conclusion - idle to upper partload system was blocked and forcing the highload system to accept the oil residue at low airflows.

The lower load system is hidden under the inlet manifold and consists of an oil separator built into the crankcase with a hose leading to a valve and tee-piece which in turn leads via two small bore hoses into two brass restricter nozzles in the cylinder head just before the inlet valves. The valve is spring loaded and NOT (in my case) the electric valve suggested in earlier replies. This system was blocked on my car and causing the problem.

After replacing all of it the problem seems, after a further 1000 miles, to be sorted.

Again the hoses were brittle with age so order before disturbing them.
The nozzles have a very small bore but are a press fit in the head so unless the head is off best to just poke them through. They are only 97p each so order them anyway in case.

I would strongly suggest the Kompressor outlet pipework and intercooler is cleaned as well as a lot of oil could be lying here and still cause problems even after the breather systems have been renewed.

Summary
The idle to upper partload oil breather system is blocked and forcing the highload oil breather system to accept the excess oil residue at low airflows.
The excess oil is then being dumped into the air filter housing then travels via the intercooler and associated pipework to the MAF.
The MAF dies!


The DIY repair. as carried out by jamesmc

Parts to be ordered prior to the work:-
1 x Main hose - MA111 018 15 82
1 x Valve/Tee-Piece complete - MA111 010 00 91
2 x Small bore hoses - MA 002 094 01 82 (supplied to me as one double length hose that I chopped in half)
2 x Nozzles - MA111 017 00 12 (These are brass)
1 Set (pair) of inlet manifold gaskets. Sorry no part numbers. These are more like silicone 'O' ring material rather than traditional flat manifold gaskets.

Tools required
A good DIY mechanics toolbox with Metric socket set will cover most of the work
Plus: Torque Wrench & Reverse Torx Sockets (for fuel rail/manifold bolts)

The Job
I haven't gone over every finite detail here but it stands to reason that any cables/connectors that hamper access along the way need to be disconnected.

• Disconnect any necessary pipework... fuel lines etc. from the fuel rail.
• Remove all the inlet manifold bolts including the two extended reverse torx bolts which, as well as securing the fuel rail, also act as manifold securing bolts.
• Ease the fuel rail out of the way
• Ease the manifold off and away from the head to one side, but don't remove it completely.
  Pulling the manifold away from the head and to one side a little gave me enough access to do what was needed. I suspended the bulk of the weight from the bonnet using bungees so that (in effect) it was floating, almost weightless, to one side.
• Remove the two small bore hoses along with the 'T' piece and the main hose.
  Both of the small bore hoses (MA 002 094 01 82), which connect to the underside of the nozzles (MA111 017 00 12), were brittle as mentioned earlier in this thread, hence the need to ensure you have all the parts required before getting stuck into this job.

The brittle small bore hoses simply snapped off with very little effort.​

Look in the images below and you will see the original small bore hoses fitted with the 'T' piece in place​

• With a pair of small light duty side cutters snip off the rest of the brittle hose remaining on the underside of the nozzle tube connectors.

On inspection, and with a squirt of WD40 via a small tube up the disconnect nozzles, I noted that the forward brass breather nozzle was about 90% clogged and the rear nozzle 100%. So not a lot of breathing going on there!

This is the forward brass nozzle that was about 90% blocked​

You can also see the original small bore hoses and 'T' Piece in place​

Another shot of the forward brass nozzle that was about 90% blocked​

also showing the original small bore hoses and 'T' Piece in place before removal

Looking directky from above at the rear brass nozzle that was 100% blocked​

After inspecting the existing nozzles, even though I had two new replacements, I decided to leave them in situ. In my mind that was the safer option rather than trying to extract brass from aluminium that had resided (mated in that position) since they left the factory in 1999.

• Check the bore size of the new nozzles and select a drill bit that matches the bore size.
• Clean the existing nozzles out in situ using a small drill bit held by hand only. I also used tooth picks and WD40 to flush out the debris. End result? Two clear nozzles to original spec.

The Valve 'T' Piece (MA111 010 00 91) looked a bit choked up too when I investigated further. It could be cleaned I guess but the cost of a new one is minimal.

• Replace the inlet manifold gaskets with two new ones and reassemble.
• Intake Manifold Bolts are torqued to 20Nm as recommended by MB.

Additionally:

I would strongly suggest the Kompressor outlet pipework and intercooler is cleaned as well as a lot of oil could be lying here and still cause problems even after the breather systems have been renewed.

Extra DIY pointers: How to Clean your MAF by Parrot of Doom


For further reading check out thread Oil In Air Intake thread

 

[jimsinessex]

Latest

As a follow up I would add that I have now covered another 55,000 miles since replacing the breather system under the inlet manifold without a single misfire or MAF problem.

Jim

 

[Blobcat]

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