Motor oil coating the air intake system!

DaveK · 19th May 2004, 03:13

Background: A while back when my M5 wouldn't pass smog I tried cleaning my MAFS with contact cleaner. There was no change that I could detect, and it didn't fix the smog problem (new cats did, but just barely). I don't think I had cleaned the MAFS effectively. I didn't take them out of the housings, and I don't think much cleaner got where it needed to go.

I think the car is down on power, so I was going to give the MAFS a more thorough cleaning today with soapy water and isopropanol as suggested in another recent thread, when I found that they and the whole intake system were coated with motor oil. Oil was leaking out where the sensor housing connects to the driver's side air filter box, and when I opened it up, I saw that motor oil had gotten on the air filter, and into the bottom of the box below it. I removed the hoses that connect the MAFS to the plenum and found oil in them as well, on both sides. Oil hadn't leaked all the way into the air filter box on the passenger side, but it got into both MAFS housings. I took the plenum cover off and saw that not only was oil pooled a bit in there, but it has coated the velocity stacks and even gotten on the underside of the plenum cover.

When I attempted to clean the MAFS before, there was no oil in them or the air cleaner boxes at all, so this happened recently. I had the dealer change the oil recently, so I checked the level and it was over the high mark, about 1/3 of the way between it and where the plastic widens (it's hard to see in the picture because of glare). Could overfilling have caused this?

I didn't bother cleaning the MAFS. I just took these pictures, put it back together, and called the dealer. I have an appointment tomorrow. I doubt this could have done the MAFS any good, but is there any other damage that could have been done? Is there anything specific I should have the dealer look for?

- Dave

Pictures:

Air filter stained with oil, oil in the driver's side box, on the tube in the cover, on the MAFS housing, etc. Also, notice that the cylindrical rubber gasket in the driver's side plenum connector tube is pushed in and kinked, sticking a bit into the air stream. This can't be good for airflow. I have no idea how long it's been that way since I didn't open that part up before, but it's not related to the oil problem. I'll ask the dealer to put a new one in.

Pete · 19th May 2004, 03:32

While too much oil can cause excessive pressure in the oil resevoir I cant believe that this alone would cause that kind of bypass of the piston rings. You might want to ask them if a broken ring can cause this. Just a wildass guess here.

FAST 5 · 19th May 2004, 04:02

Dave,
What year is your car?
Robert

DaveK · 19th May 2004, 06:36

Quote:

Originally Posted by FAST 5

Dave,
What year is your car?
Robert

It's a 2000 model with 69K miles on it. I've only had it a few months, and it has the CPO 6yr/100K mi warantee.

- Dave

jaj · 19th May 2004, 06:41

My '01 M5 had this problem once - I got an SES light and when the dealer opened up the air filters both were full of oil. The diagnosis was a failed rubber O-ring seal between the VANOS actuator body and the cylinder head that was leaking oil into the plenum. New O-rings fixed it.

Cheers
JJ

DaveK · 19th May 2004, 06:49

Quote:

Originally Posted by Pete

While too much oil can cause excessive pressure in the oil resevoir I cant believe that this alone would cause that kind of bypass of the piston rings. You might want to ask them if a broken ring can cause this. Just a wildass guess here.

Pete,

Thanks for the response.

So you think it's oil bypassing the rings into the combustion chamber, and out the intake valves into the plenum? That sounds pretty bad.

How could that happen though since the pistons should be sucking air in while the intake valves are open, not blowing anything out through them? Wouldn't oil in the combustion chamber be burned and blown out the exhaust instead? I haven't noticed a cloud of blue smoke behind me or smelled anything funny, but of course I wasn't looking.

- Dave

DaveK · 19th May 2004, 07:16

Quote:

Originally Posted by jaj

My '01 M5 had this problem once - I got an SES light and when the dealer opened up the air filters both were full of oil. The diagnosis was a failed rubber O-ring seal between the VANOS actuator body and the cylinder head that was leaking oil into the plenum. New O-rings fixed it.

Cheers
JJ

Thanks, JJ. This sounds promising. Was there any damage? Did they replace the MAFS because of potential fouling, or anything else?

I got an SES light a few weeks ago and went to the dealer. They found that there were codes still there from when the car wasn't passing smog and the cats were replaced (the other dealer forgot to reset the codes), so they cleared them and said to come back if it came on again. That's when I had them change the oil. I think the SES was related to the emissions problems because the codes were for cats & exhaust sensors. The SES light hasn't come back on, but if this continued much longer and soaked the filters and MAFS more I bet it would.

- Dave

jeeperjohn · 19th May 2004, 07:27

Dave,

I think Pete is talking about the pressure inside the engine building up due to pressure leaking past the rings. You might have a plugged crankcase vent causing the pressure to force the oil back into the plenum via the valve cover vents located at the front of the plenum. Or, the issue JJ talked about sounds likely to.

Good Luck, John

Quote:

Originally Posted by DaveK

Pete,

Thanks for the response.

So you think it's oil bypassing the rings into the combustion chamber, and out the intake valves into the plenum? That sounds pretty bad.

How could that happen though since the pistons should be sucking air in while the intake valves are open, not blowing anything out through them? Wouldn't oil in the combustion chamber be burned and blown out the exhaust instead? I haven't noticed a cloud of blue smoke behind me or smelled anything funny, but of course I wasn't looking.

- Dave

2003 M5!!! · 19th May 2004, 07:37

I noticed oil on my air filters recently too. The car seems to be running fine and the oil didn't seem to be all the way up into the MAF -- just at their openings and on a 2 inch portion of the air filters. The only reason I noticed it was that I was putting in my K&N filters.

It looked more like oil was sucked up into the filter, but this wouldn't make too much sense either. Sometimes I wash my engine (which collects significant oil in LA) so maybe after I washed it some oil/water was sucked in?

If there is a problem, I am hoping the SES light will come on . . .

Please keep us posted on what the dealer says is wrong.

P.S. About a month ago my oil pres. light came on. The dealer said it was a faulty signal. Sometimes I get the impression that the dealer doesn't know what is up either.

Quote:

Originally Posted by DaveK

Pete,

Thanks for the response.

So you think it's oil bypassing the rings into the combustion chamber, and out the intake valves into the plenum? That sounds pretty bad.

How could that happen though since the pistons should be sucking air in while the intake valves are open, not blowing anything out through them? Wouldn't oil in the combustion chamber be burned and blown out the exhaust instead? I haven't noticed a cloud of blue smoke behind me or smelled anything funny, but of course I wasn't looking.

- Dave

DaveK · 19th May 2004, 07:46

Quote:

Originally Posted by jeeperjohn

Dave,

I think Pete is talking about the pressure inside the engine building up due to pressure leaking past the rings. You might have a plugged crankcase vent causing the pressure to force the oil back into the plenum via the valve cover vents located at the front of the plenum. Or, the issue JJ talked about sounds likely to.

Good Luck, John

Thanks for clearing that up, John. It makes a lot more sense to me now.
Hopefully that's not it, bad rings would be a worse problem than the issue JJ had. I'll suggest that the dealer do a compression test. I'll let you all know what they find.

- Dave