Question on oil filler cap
 

I noticed I have oil leak coming out of my oil filler cap and made a mass on top of the engine in my W124, especially after a long drive. It seems the problem may be more severe than I thought because I can see oil residue on the hood pad as well. Do I need a new oil filler cap? Do any of you change any of the caps in your engine compartment? I read it once that it is advisable to change all your caps - oil filler cap, radiator cap and gas cap every so often. Any suggestions?

87 W124
95 R129
98 W163

If I remember right, there is an improved version of the oil cap. A few $s.

....replace the cap....but keep checking it for a bit, if it's still leaking you may have a crankase venting problem.....:p

The first thing I would check is your crankcase ventilation.
There is no way a leaking oil cap could produce the amount oil you describe with out your crankcase being pressurized!!
I don`t know if you have a PCV valve or a just a vent with a filter.Your oil cap itself could house the filter and be clogged.

Check and repair it before you run yourself out of oil.

John

OK guys, what is this crankcase ventilation? This is the first time I have ever heard of this. The symptom I have here is oil leaks on top of my crank case, and oil spots on the hood pad. The gasket on the oil filler cap does look pretty shot but I have no way of knowing if that's what causing all the oil stain on my crank case. Not unless I ride shot gun in the engine compartment. How do I check this ventilation? What effects it has on the engine itself? Thanks for any information.

87 W124
95 R129
98 W163

Sorry this took so long.Our yellow Lab was paralyzed yesterday,and we were at Tufts Veterinary School visiting him.
As your engine runs because of the volume of the crankcase that does not contain oil pressure is created. If its not vented in some the pressure becomes extreme. Years ago before emission laws, it was vented directly to the atmosphere. Today its called a closed system where it is vented thru a positive crankcase valve or PCV. This allows it to enter the combustion, be burned and and exit the exhaust.
There should be a hose running from one of your valve covers to your air cleaner. At the valve cover should be the PCV valve, this is most likely what needs to be replaced.Open your air cleaner and there should be another small filter . If you have oil inside the air cleaner that's also a sign.
A PCV should be under $20.00,pop in pop out no mechanic. also check that the hose is not clogged. This hose my not go to the air cleaner, but it goes to the intake at some point.
I hope that's your problem. Check your oil!!!

John

Elau:

Although you MAY have PCV problem, but the defect oil cap on the W124 is a well know problem and that is why Mercedes released a improved version for it (see my original answer to your question).

I quote a written line from a MB tech with 30 year experience on this:

"Mercedes has a new style oil cap which does not leak - for all models at about six dollars. This is a must-have item. "

So go buy one and see if it still leaks.

Hi Bo,
I had never heard of that, it could be the fix.
It seemed to me that the amount of oil was too exsessive to be the cap
Thats why this forum is so good, everyone has different experiances.
Glad to report that Sonny our Yellow Lab,supported his own weight this AM!!! Seems on his way to recovery!!
John

I have done that on my previous 1990 300E. It leaked oil on the cap and a new one fixed that. The new one is also plastic but it does look a little different.

Then I ordered one for my 1991 300E just to feel safe. It is very inexpensive.

Speaking of caps, I have replaced the coolant expansion caps as well. About $5 each (every 80 - 100kmi) and makes me sleep better.

Went ahead and bought a new oil filler cap and gas cap. The oil filler cap costs $6 and the gas cap $8. The new oil filler cap does look different than the old one. Now I just have to see if that takes care of the problem. Will take the car out for a long drive Sunday. Thanks for everybody's input and I will let you all know how the new one works.

87 W124
95 R129
98 W163