would like the forum's opinion on why a diesel engine will stop running if the valve cover vent is blocked? a couple years ago some one mentioned that this was a good test to measure the blow by of a mercedes engine and it does give a decent indication of the amount of blow by gases.if engine stops earlier than 10 seconds after blocking the blow by with a finger it shows potential wear problems(my experience) keep in mind that this method works to shut down a engine with or without an alda control valve.
i think that the engine just sufficates from the unburnt blow by gasses thru the valve seals and would like to hear some other opinions.
larry perkins
68 old mercedes(just added 3 from gene2's collection)

Larry,

I always wondered about that too. But I don't think enough blowby gasses could get thru the valve seals to effect the engine much. Seems like somehow it would have to shut off the fuel but I don't know how pressure in the crank case would do that.

Maybe someone here can give us a good answer.

P E H

the shutoff valve! Pressure in the crankcase is the same as vacuum outside the crankcase, because the shutoff diaphragm is vented to the crankcase. Blocking the blow by will, eventually, cause the shutoff to function.

I guess that timing this process is one way of quantifying the blow by, with a longer time indicating less blow by.

__________________
Alan the Radio Guy
--------------------
Amateur Radio Station N7CEU
1985 300CD 199,000 and still rolling

Radio Nut,

That makes sense that pressure in the crankcase causes the shutoff valve to close and stop the engine if the shutoff valve is vented to the crankcase. Pressure on that side of the diaphram would do the same thing as vacuum on the opposite side: Shutoff the fuel. So I was correct in my assumption that crankcase pressure shut off the fuel, I just didnt know how it happened.

I wonder if it was designed that way to shut off the engine if the crankcase becomes pressurized by some failure in the engine such as plugged vent system or a hole in a piston. Or maybe so the blow by could be easily tested.

P E H

P.E.H.,
IIRC, earlier IPs on OM61* engines were separately lubricated and not vented to crankcase. In these, the blowby gases would not cause engine shutdown.

The answer to whether it is a "design feature" or not, is to see whether it is documented in the service manual for the first OM61* engine using the shutoff valve in a crankcase vented IP.

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

just a fact to add to our discussion, i have at least 10 of the 69-73 220d cars with the 615 engine that has the ip with its own lubrication and i can tell you that the engine will shut off the same way if you block the valve cover vent. these cars have the throttle body to create the vac for the control of the fuel .
thanks for all the input, am learning.
larry perkins
68 old cars