A crankcase explosion occurs within the engine's crankcase......usually caused by a very hot bearing, or a very worn set of piston rings and liners, heating the lube above it's flash point.....this ignites all of the oil vapors within the engine.....and makes a very loud noise!!!! Occasionally, fuel oil mixed with the lube oil will either cause, and/or exacerbate the explosive mix.....

As the theory (safety/fire prevention) goes .....if you maintain a slight positive pressure (about the pressure that natural gas is in your stove) then....in theory the atmosphere within the crankcase will remain basically static and unmixed with oxygen, thus preventing the formation of a combustible mixture (fuel/air ratio).......if a slight vacuum were within the crankcase it would suck air/atmosphere into the crankcase at various points and allow a combustible mix to form.....and then when a source of ignition presents itself....Boom.....

Trust me, it would make the housekeeping/cleaning of the engines if this were not so.....the slight positive pressure pushes oil out of the engine....

On the side of every industrial engine that I have worked on, there is a Warning Sign.....that reads something like this....."The engine must be stopped for a minimum of 5 minutes before opening the inspection doors"

In the case that I was involved with....MAK engine....we had fuel contamination of the lube oil......this was known, and an oil change was denied by the "powers that be".......I had gone on record "she's gonna blow up, sooner or later"......and she did....when it did, it blew open all of the explosion doors, it blew the gasketing from behind the explosion doors, it also blew the cylinder liner seals from 3 of the cylinders (this allowed the jacket cooling water to flood the crankcase, this interrupted cooling to the rest of the engine).....it also ignited the bilges, FIRE big time!!, and was the only time I ever had to drop CO2 into the engine room......was a very amazing event.....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

SB,

Very interesting. I guess I had incorrectly thought of diesels are sort of explosion-resistant when compared to other engines.

dd

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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

Shorebilly,
Thank you for the explanation, I learned something, That absence of oxygen is the ticket. Can bearings get that hot and still survive or are they damaged already and get overheated as a result?

thanks again,

Johan

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85 MB 300TD with om616 4 spd
83 MB 300TD
83 MB 240D scrapped
82 MB 240D scrapped
97 Ford E350 diesel 4x4, WVO
94 Ford E350 4x4 diesel blown head..parts car
85 cherokee diesel 2.1, 300.000, WVO
85 cherokee diesel 2.1
85 lebaron convertible, to be electric
85 lada niva 4x4 with 1.9 peugeot diesel,
72 citroen DS 5spd, LPG
77 Jaguar XJS, LPG
73 corvette 350 auto
88 MB Gelande 240 GD military
98 Ford E350 mini bus to be new 4x4 camper

On the original question-the cleanliness of your IP and injectors has a HUGE effect on blowby and ring sticking-I finally did the Diesel Purge on mine, and combined with synthetic motor oil (Royal Purple Longrider 15W40 right now) she's doing a LOT better-I have a Motor Guard toilet paper bypass filter that I'm going to install soon and go to Delvac 1, hoping that it keeps things clean enough to improve my cold weather starting ability.

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K

In the past half century, a lot of people have driven a lot of MB diesels to death, but I've never heard of any blowing up.

I'm not saying it doesn't happen in industrial engines, and I'm not saying it couldn't happen if you actually tried to do it to an MB, but I'm not worried about it.

Somebody get a hold of Mythbusters to see if they can blow up a Mercedes.

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1982 300CD Petrol/Black Leather

As I stated earlier, I was unsure if the vacuum pump discharge into the crankcase was a "design consideration" when MB designed the OM 617.xxx engines......was just putting forth a possible reason for doing this....

Then I got into answering questions.....

Usually, if there is a crankcase explosion.....something was bad wrong beforehand.....and it is a phenomena of "large" Diesel engines......I would imagine it can happen in any Diesel Engine, however would most probably be unlikely in an automotive application.....please bear in mind that the industrial engines, no matter the application, tend to run continuously for long periods of time...days, weeks, months......and generally have thousands of more hours on them than the average automobile......even long haul trucks.....!!!

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

Interesting. I just had my injectors overhauled...interested to see if this has any effect once they break in.

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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

Mine has had major blowby/driveability problems in the 20K+ I've had it, rebuilt injectors & a new rack dampener pin had almost no effect, syn oil helped somewhat but improvement disappeared when I went back to dino oil-only the Diesel Purge has helped-the best $35 (with new fuel filters) I've ever spent!!

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K

In my continuing quest to try to understand what my engine is telling me...

Start engine, instantly pull off oil cap. No oil mist in blowby, put hand over oil filler hole and theres very little air coming out. Looks ideal.

Within 30 seconds oil (or diesel?) (gray-ish, not blue)mist appears and puffs more out of the cover. It puffs more than other 676/617's Ive seen.

What could that mean? If it was low compression, wouldn't the blow-by reduce as the engine warmed up due to ring expansion?

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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

In my very limited knowledge...

If your engine starts and runs well, doesn't noticeably blow blue smoke while driving, and doesn't have a HUGE oil consumption problem, then you probably don't have too much to worry about. I remember reading the technical specs for oil consumption on the 616/617 published by MB, and the allowable amount of consumption before the engine was considered out of spec was RIDICULOUS. We all like our cars to perform like they are new, but they fact is if you have ANY OM617 it has to be at least 22 years old. By the standards of any other vehicle, a 22 year old engine is pretty old. My engine is 31 years old. It uses 1/2 to 3/4 of a quart between changes, depending on my driving habits. But it runs nicely, starts in the cold without a block heater, and is reliable. I can't ask for much more from a 31 year old engine.
These cars are old. Just because they are Mercedes doesn't mean they will perform like spring chickens forever.

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http://www.betten.mercedescenter.com...n_banner_1.jpg
1976 300D
190,000 Miles
Colorado Beige

1975 300D
Parts Car
78,000 Miles
Rustbucket
Also Colorado Beige

1984 190D 2.2 (Dad's)
156,000 miles
Champagne Metallic Clearcoat

Is it possible to put that much weight in this "tea-kettle" test? Unless you are consuming a large quantity of oil or some other malady, what is the point? Isn't the only true test for "blow-by" parameters a compression test?

Other factors involved are weight/type of oil, vacuum pump, outside air temp, valves, and others.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I am surprised that nobody has picked up on F18's tip. These older Diesels that consume oil could greatly benefit from this tip. I will try it on mine at next Valve Adjust time. All of the experts have been claiming for years that it is due to Valve Guide wear. I cannot buy this explanation when an engine is using 1 qt per 300 miles and there is no blue smoke ever.

Something that has not been stated. Some "blowby" will always occur due to the movement of the pistons up and down and acting as an airpump in the crank case. It is a dynamic situation that does not fully self-cancel. In addition to this is the contribution from gases coming past the rings and the vaccuum pump discharge as already noted. In general blowby is a very poor and unreliable diagnostic and this has been noted in some of the threads dealing with compression.

Please jump in here some of you guys since I want to learn more on this topic. The info on the industrial large diesel engine explosion feature was very informative.

I don't know about later vacuum pumps but the claim that the vacuum pump vents into the crankcase on the early model vacuum pumps seems false. The early model vacuum pumps have a line that vents into the top of the air cleaner.

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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