Oil Vapor Getting Past Filler Cap - PeachParts Mercedes-Benz Forum

sasquatchgeoff · #1 10-22-2008, 12:21 AM

I have replaced the cap with OEM, aftermarket caps and still get a lot of vapor bypassing the gasket on the cap. Is this normal? Seems like the EGR system should prevent this.

I tried a pretty good search but got no answers - scold me if there is something out there to answer my question.

- geoff

#2 10-22-2008, 12:29 AM

The EGR is for emissions, it has nothing to do with the crankcase gasses.

Put some high temperature wheel bearing grease on the cap's seal.

Jeremy5848 · #3 10-22-2008, 12:30 AM

The EGR system has nothing to do with oil vapor – you mean the crankcase ventilation system. In any case, are you sure that the vapors are coming from the oil filler cap? They could be coming from the elbow that connects to the port in the valve cover, next to the filler cap. The elbow, originally rubber, turns to hard plastic over time and can crack and leak. In the 61x engines there is actually an aluminum "pipe" (part of the casting) over which the elbow is clamped but in the 60x engines the elbow fits into a hole in the cover. Once it turns hard, the elbow can be difficult to remove without bits and pieces falling inside. There was a thread on that subject here a few months ago to which I contributed.

Leaking caps have also been reported here. Some people have reported success with two gaskets but I would think that would suggest a cap that is fitting too loosely; whether this is a cap problem or a valve cover problem I do not know. Any cap leaks I have had have been fixed with a new rubber gasket.

Jeremy

sasquatchgeoff · #4 10-22-2008, 12:42 AM

As for EGR - I stand educated - crankcase ventilation is the issue here. I gingerly removed and cleaned the elbow, thinking it may have been stopped up creating a backpressure situation on the filler cap gasket. I think I will try the two gasket method.

I really appreciate the quick response and help - I have never been let down by this forum. I wish I could say as much for my cars.

GRIESL · #5 10-22-2008, 09:40 AM

Possible that it's not vapors escaping and making the mess. If the filler cap on the 201 is like the 123, don't turn it upside down when you take it off to fill 'er up with oil. The oil drains into the cap and when you put it back on the valve cover, the oil drains out of the cap and onto the valve cover and makes a mess.

charmalu · #6 10-22-2008, 01:35 PM

I vote on replacing the rubber seal under the cap. I din`t see how 2 will fit.

The rubber seal like the rubber elbo next to the cap are both exposed to heat and oil which over time cooks them.

Maybe the 2 tangs that lock under the valve cover are bent enough to not let it fit tight.

Charlie

The Gears · #7 10-23-2008, 11:17 PM

If you look at the cap yu will see that there are an outer part and an inner part pressed in place. See the rippled edge on the inner cap. That part is outside the gasket. The oil goes inside the cap at the two closing springs, fills the cavity between the two parts and comes out the ripples all over everything. I tried two gaskets, they won't let the cap close. The Easy fix. Boil the cap to remove all traces of oil. then with a small screw driver or other small blade fill the spaces in the ripples with some sort of a two part epoxy Iron paste, like JB Weld or similar. Worked for me.

Cr from Texas · #8 10-24-2008, 01:57 AM

Two new ideas and I'm wondering "why didn't I think of that".
Thanks

Quote:

Originally Posted by GRIESL

Possible that it's not vapors escaping and making the mess. If the filler cap on the 201 is like the 123, don't turn it upside down when you take it off to fill 'er up with oil. The oil drains into the cap and when you put it back on the valve cover, the oil drains out of the cap and onto the valve cover and makes a mess.

Guilty - for years and years but now that you point it out, it won't happen again!

Quote:

Originally Posted by gears

If you look at the cap yu will see that there are an outer part and an inner part pressed in place. See the rippled edge on the inner cap. That part is outside the gasket. The oil goes inside the cap at the two closing springs, fills the cavity between the two parts and comes out the ripples all over everything. I tried two gaskets, they won't let the cap close. The Easy fix. Boil the cap to remove all traces of oil. then with a small screw driver or other small blade fill the spaces in the ripples with some sort of a two part epoxy Iron paste, like JB Weld or similar. Worked for me.

Any chance of some JB Weld dropping into the engine? That seems bad. I've also spotted a small nick (dent) in the valve cover sealing area. JB weld or high temperature grease?

rrgrassi · #9 10-24-2008, 10:54 AM

Mine does that too, and I have the plastic oil fill cap since the metal one os long gone...

Cr from Texas · #10 10-24-2008, 02:45 PM

Seems like there is an old post of someone replacing the check valve at the end of the oil seperator return tube. If this were bad, could that explain some of the accumulation of oil around the fill cap, in the air cleaner housing, and some of the drips?

sasquatchgeoff · #11 10-25-2008, 04:37 PM

OK, I think I am figuring out what is happening. I put two (2) thicknesses of gasket material to no avail. The spring in the cap is certainly allowing the vapor under pressure to bypass the gasket(s) - but the catch is, it is only at idle speed. Another revelation is that the excess vapor pressure is bypassing the cap because there is a ton of blow-by (there is a small amount of oil in the coolant). Please correct me if I am wrong on this. Here is a shot of the crankcase ventilation tube coming out of the valve cover and into the intake manifold. When the engine is a higher rpm this part of the system functions properly:

and here is a shot of the filler hole with cheap aftermarket filler cap - the OEM plastic cap performed even worse.

My crazy idea is that if I had a filler cap that would not have a spring release to allow pressurized vapor to bypass, the vapor would travel into the proper route via the elbow and vapor tube to the intake manifold. Any thoughts?

TIA - geoff

#12 10-25-2008, 05:19 PM

Put some high temperature wheel bearing grease on the oil cap seal.

sasquatchgeoff · #13 10-25-2008, 08:46 PM

After trying an extra gasket, then two extra gaskets, then hi temp bearing grease, all to no noticeable change in vapor bypass, I tried the fuel filler cap and it stopped the vapor! The fuel filler cap had the Mercedes three point star in circle logo - which told me it was a factory part. I simply put the cheap aftermarket Chinese oil filler cap on the fuel filler tube. Problem solved.

Thanks to everyone who chimed in - now on to the oil in coolant problem...

- geoff