What is the white crude under my Oil cap?

Eric Mckenna · 06:44 PM

Hey Guys,
What in the hell was the white / yellow-ish crud I found under my Oil cap today. The car has been sitting for a while and I just took her out again today.. I have never had this before as last year I drove the car in the winter.. is this from sitting?

Eric

MBAtarga · 01-04-2003, 06:37 PM

Yes it's from sitting - water condensation. Get out and drive that car til it's nice and warm!

Eric Mckenna · 01-04-2003, 06:43 PM

I did that today as a matter of fact.. drove it for about 3 hours ... I was just wanting to know what it was. hahah I know the car ran great! so I was a bit puzzled by this crudy stuff. hahah Thanks for the input on it.

Eric Mckenna
78SC

Jbabic · Jbabic's Garage

Don't Worry, I have the same, its what water/condensation and oil look like together.

Tom F2 · 01-04-2003, 06:57 PM

It's crankcase vapors condensing on the cold oil cap. It happens to me all the time in winter, whether I drive long or short distances, provided the temperature is cold enough. My oil cap actually got very rusty this way!

911pcars · 01-04-2003, 06:59 PM

It's "sludge" which is made up of moisture, unburned fuel, byproducts of combustion, carbon, etc. Sludge forms when the engine runs but seldom gets up to operating temperature. If the engine constantly operates under these conditions, sludge will cover engine parts and inhibit heat transfer, accelerate wear and perhaps block oil passages. Changing oil and filter more frequently is the solution.

On water-cooled engines, it could also be a sign of internal water leakage from a bad head gasket, cracked cyl. head or block.

Sherwood Lee
http://members.rennlist.org/911pcars

MotoSook · 01-04-2003, 07:37 PM

I wonder if removing the oil cap for a few minutes after a warm up drive (hot enough to vaporize the impurities) would be a useful method to keep the oil cleaner, longer. The fuel and water will boil off at a lower temp then the oil, so letting their fumes escape would be a small step toward preventing buildup and oil preservation. Anyone think this is crazy?

Tim Walsh · Tim Walsh's Garage

hmm.. doesn't sound too bad.. but I'd worry about spillage and contamination....

yep in water pumper it can also mean a warped head... it happened on my old truck

Eric Mckenna · 01-04-2003, 09:37 PM

Nope it has no H2O it's a 78SC..

Eric

MotoSook · 01-04-2003, 09:45 PM

The water I refer to is present in the condensation inside the oil tank....I guess some H2O is there right? Water is a by-product of combustion, so if you have soem blow by and some of it contains water vapor, well, it might end up in your tank????? Opening the oil cap, even if you have not H2O.vapor in your tank at that time, would still let the lighter impurities (vapor) out, no?

Eric Mckenna · 01-04-2003, 09:51 PM

Souk,
I will try this method you're talking about. and see what happens, altho i am not sure if I'll see much as i have never seen this before on my car.. as i normally drive it everyday and the drives were about 2 hours everytime or more.. this is the first time it has been put up in the winter. so this new to me. next time I go out i'll leave the cap off for a while and see if this eliminates the crud from forming..i'll post my results to this thread. but yeah what you had said sounds good in theory but i'll have to see if it works.

Eric

911pcars · 01-04-2003, 10:14 PM

You shouldn't have to regularly remove the oil tank cap to "aerate" the engine. If the engine gets up to operating temperature on a consistent basis, the water vapor will evaporate. If you don't or can't, plan on changing the oil more frequently.

Sherwood

Tom F2 · 03:25 PM

WADR, Sherman, I am afraid that the foamy oil cap is something that just won't happen in SoCal, reason being it's too warm. In our frosty climes, the ambient air is cold enough to chill the oil fill cap, thereby promoting the condensation of water from the combustion process into the oil/water emulsion that we find there. It will happen no matter how much you drive, if the temperature is cold enough. I wipe down the inside of my oil filler cap every few days during cold weather driving.

I learned about chilled crankcase vapors servicing MBs. For those old enough to remember, this form of condensation created some sensational problems on early injected gas Benzes. The crankcase vented to the throttle body, which was way out on the intake manifold in the chilly air. Not only would the crankcase vapors condense there, they would freeze, and stick the throttle open! Benz (who were the only company who ever understood mechanical injection for Otto cycle motors) remedied this with a water line to the throttle to keep it warm.

BTW, I am NOT getting much of a chance to drive, this winter, which has been snowy since early December! I don't take the precious out on salty/snowy/icy roads.

P.S. Don't drive with the oil filler cap off.