with the oil filler cap removed, I notice my 83 240D has a lot more oil blowing out of there than my 83 300D turbo. Also, the cap jumps around a lot more on the 240D. I looked at another 240D and noticed the same thing.
I assume the 300D turbo has lower compression ratio being a turbo. Could that account for the difference in blowby?
My 240D runs great otherwise, very peppy, exhaust looks clean & does does not smell of burnt oil. no smoke under hard acceleration.

Are there other tests that I can try?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

It is what it is.

And you cannot change what it is for anything less than a small fortune.

So, why bother worrying about it?

Very true. I am not losing any sleep over it. Just want to learn more about these fine marvelous machines.

I am really enjoying driving the 4 spd manual 240D. Just put on a set of new 175 70R14's on the 5.5J 14 alum rims. The car is very responsive. Ahhh manual transmission I love it.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

In answer to your question, no. No reason I can think of that a 240 would have more blowby unless it is worn more.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

My 240D also has noticeably more blow-by than my 300D, which surprises me because the 240D is a fully-documented one-owner with 130k miles while the 300D has no known history and a broken odometer. Both run great, though, so I'm not really worried about it.

All things being ideal, a 300D will have more blow-by because of it's larger displacement and additional cylinder.

The 240D has 21 to 1 compression ratio. What is it for the 300D turbo?
Would new valve system seals lessen the oil mist and blow by?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

300D is 21.5: CR.

Valve stem seals will not alter blow-by because the pressure difference will not push air into the valve cover at idle.

yep.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Is there anything you can do about blow by? What causes it?

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1984 300TD

Two main things are contributing to blow-by on the Mercedes Diesels
1: The vacuum pump is continuously pumping air out of the vacuum system and into the crankcase.
2: Worn engine, specifically the wear of the piston rings.

The only way to reduce it is an engine rebuild. Please note that ALL engines have blow-by, even the brand new 2008 CDI diesels.

As long as it runs well and does not consume excessive amounts of oil, there is no point in worrying about blow-by. The only times you should worry about it are when you are inspecting the vehicle for purchase and if there is a serious running problem with the engine.

For some additional reading: Blow-By curioisty questions

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

occaisionally running some lucas oil treatment in the car will free stuck rings. I have tried it several times. It has not hurt anything in my case but did not help either. Mine turned out to be more than stuck.

WVO conversions are thought by some to cause stuck rings.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Isn't this only the case on later vacuum pumps? On early pumps, the air feeds into the air cleaner and not the crankcase I think.
It might be interesting to compare different pump systems for amounts of blowby.

Correlated with this, does a vacuum leak produce more blowby because the vacuum pump has to work continuously to keep up??

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Under "normal" conditions, the airflow produced by the vacuum pump is negligible. Once the system achieves 20", the only continuous leaks are the brake booster (when you step on the brakes) and the transmission control (negligible).

Even when the system is not up to par and the pods are leaking, the volume is insignificant when compared to the typical leakage past the pistons. The only way you'd get significant blowby from the vacuum system is to disconnect the main line to the booster.

The vacuum pump works continuously to maintain 20" vacuum, whether there is airflow or not..........it really doesn't care.