Why is My 420 SEL Blowing Lots of Oil from Dipstick

My 87 420 SEL with 200K has been running fine, no problems and no oil consumption. The other day it dumped, literally, several quarts of oil out of the dipstick hole...obviously there is some pressure build up in the crankcase...I don't think it is blow by because this was so sudden and so dramatic...I can't see anything wrong except the air pump is not working but that has been the case for some time. According to the Mitchell's book, the crankcase vent system looks pretty simple but Mitchell's doesn't explain the connection between the hose from the valve cover and the mechanical cylinder that it hooks into...my guess is that what is happening is that there is an electrical problem that is closing off the mechanical cylinder and not letting the crankcase vent properly. It only does it when under power, not when idling. Its a mess, though, and I can't drive for more than a couple of miles without all the oil shooting out of the dipstick hole...that doesn't sound like blow by to me.

Thanks in advance for any suggestions.

[mbdoc]

The only engines that I have seen expel like that have had excessive oil levels. After this happened where was the oil level? Any recent service work, & or has engine ever been overheated?

The oil level is below the stick afterwards...and the oil pressure drops from 30 to zero...I have had this car for about a year and haven't had a bit of trouble...no service work or overheating....no excessive oil consumption... nothing.

I am a fairly handy shade tree mechanic but haven't seen anything quite like this...then again, I never have had the pleasure of figuring out German engineering...which hear is remarkable. I still think that there is some "switch" that must allow crankcase gases to circulate from the crankcase into the fuel injection system and that switch is not working.

[mbdoc]

There is a PCV orfice in the intake manifold. The rubber hose from the left(drivers) side valve cover connects to this orfice. The orfice is supposed to be 1.5mm (.060") in dia. But it sounds like the oil is foaming & causing the level to rise. I would want to change the oil & make sure that the level is correct with 8 qts of fresh oil! Possibly the oil is being diluted with fuel? Happy Holiday

A consideration may be a cylinder leaking compression down to the engine, increasing the internal pressure and subsequently sending oil trough the dipstick tube.

[Benzmac]

There is no electric or mechanical valve that allows crankcase ventilation. IT is done through two hoses on the valve covers. One per valve cover. One hose connects to the air cleaner housing and the other, as Doc explained, is under vacuum at idle and has a hole in it for this reason.

I would check those hoses, I would think that one or both of them has collapsed. I have seen this on later v-8's/

[be459]

Do a compression test as suggested by lobito. A broken ring(s) can do that too.

Happy holidays.

David

Bob Ford, in reading your remarks, and what you think it ain't let's think of what it is. Have you removed the filler cap in an attempt to releave this high pressure? Can you hear any pumping sounds from the crankcase when the filler cap is off? Does the exhaust sound normal? How about the cooling system level and collor(any oil there?)? If it were me I would drive with the filler cap removed and a piece of cheese cloth afixed at the opening, this will stop any oil from being blown out from the overhead oiling system and crankcase pressure. You have a regular Hitchcock so stick to it and maybe others will be able to had to your help wanted. Happy Trails Beep Beep from Houston.

Donald
somemore blow hard whoops I'm meant Blow-by

[jeffsr]

Several quarts!!!! Wow. That really sounds like drastically high crankcase pressure. Bad head gasket or broken ring. If what you describe is true, then I don't think the PCV system is going to be able to handle it..
"It only does it when under power, not when idling" This is also kind of a clue as to what is going on. I'm betting on head gasket. Have the compression checked as advised earlier..Let us know.

[420SEL]

I had the exact same thing happen to me two Christmases ago. We were driving from Toronto to Halifax after the holidays (2 day drive). We stopped in Quebec city overnight and the temp was down to -30 C (about -25 F). The next morning I started the car up, and in about half a minute the oil pressure guage dropped to 0. I immediately shut the engine off (hadn't driven anywhere, just warming it up) I checked under the hood and there was a lot of oil all over the place, especially on the hood pad over the dipstick. It was those breather hoses that go to the top of each valve cover. A lot of short trips had built up a lot of condensation in the engine adn it gooed up those hoses pretty good, that combined with the freezing temperature (which solidified it) caused the oil to blow out the dip stick. It took a good 6 quarts to fill it back up (takes aty least 8 quarts at an oil change). I had the car towed to a loacl garage (MB dealer not open on Sundays). It took several hours for the car to thaw inside the garage. They took off the valve covers and they were lined with a white gunk, same with the hoses. They cleaned them all up withsome kind of cleaner they had, put everything together, filled up the oil and we were off. I had my mechanic check it after we got home (11 more hours of driving). Fortunately there was no damage done, and it hasn't caused a similar problem yet. I now check these hoses and the oil filler cap for the white gunk twice a week. As winter was coming on I noticed it starting to build up again, but two or three hour long highway runs a week seems to get the engine hot enough to clean this stuff up. That was my problem, yours might be different, but for sure get it looked at. Good Luck.

With your help I was able to track down the culprit---that little 1.5 mm vent hole in the Idle cylinder (or whatever that thing is called) was blocked and would not let the crankcase vent. As soon as I ran a little wire through it and knocked out the crud I was back in business...thanks for all the ideas...I am glad it was what it was.

Sometimes it is the simplest of things...you just need to know how stuff works, I guess. Thanks to all.

Bob Ford

Bob Ford, isn't this a great Forum? Everyone pitched in and your "Moderator" nailed it. Your other forum friends were there too. Happy Trails Beep Beep from Houston.

Donald.
Always here.