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#1
08-25-2009, 11:11 AM
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How much blow by is too much?
I went and looked at a couple Diesels yesterday. One was an NA 300D that had some blow by that was whitish in color, not that much but I noticed it, I then proceeded to check out a turbo 300D that also had blow by but it was blue, and about the same amount as the NA motor. I wonder if some is OK or not?
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1981 300TD 2005 C55 2004 E500 1999 ML430 1992 400E 1998 C43 2001 SL500 1988 300SEL 1986 190E 16V 1991 190E 2.6 
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#2
08-25-2009, 11:17 AM
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Let engine warm,open hood.Losen the oil cap if it shoots off maybe bad,if it rattles ok.Note: valve adjustment can improve things,and hose routing to burn blow by gases can affect cap.
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1999 w140, quit voting to old, and to old to fight, a god damned veteran
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#3
08-25-2009, 12:30 PM
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my buddy told me that if you can shut the engine off quickly by holding your finger over the valve cover vent, it's got a decent amount.
any truth to that?
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83 300SD 226k virgin.  05 chevy duramax :bowdown: air suspension + 500hp = fun for everyone 01 silverado 2wd 1500 5.9 cummins 
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#4
08-25-2009, 12:33 PM
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I've heard that too.
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1999 w140, quit voting to old, and to old to fight, a god damned veteran
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#5
08-25-2009, 01:17 PM
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From what I understand, attempting to shut the car off via plugging the offgas line is not good for the engine.
Don't think a valve adjust will affect blowby, since it is plain and simple, gasses getting by the pistons. So all lower end of the engine. Blowby is not the be-all end-all in terms of engine health, but I always check it when looking at a car, always after it's been warmed up. If it blows the cap off, I'm wary of that engine. Saw a 113K mile coupe that barely moved the cap at all, and a wagon with 300K where it blew the cap right out of the engine bay.
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I-------------------------------------1981 300TD, Thistle Green, 140K------------------------------------I
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#6
08-25-2009, 02:53 PM
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Answer
Run away diesel, why does it happen?
http://www.peachparts.com/shopforum/showthread.php?t=101404 Have a great day.
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ASE Master Mechanic asemastermechanic@juno.com Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 1984 190D 2003 Volvo V70 2002 Honda Civic https://www.boldegoist.com/
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#7
08-25-2009, 03:29 PM
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MB made a tool for measuring blowby. I assume there are limits related to that tool.
Some years ago, a thread was started on this forum in which blowby was measured in the number of seconds the engine took to pressurize a 30 gallon trashbag. Not a bad comparative process in my view. Here's the thread: http://www.peachparts.com/shopforum/showthread.php?t=193602&highlight=blowby+gallon Pinching off the PCV hose and pressurizing the crankcase has very limited value because it presumes that all crankcases have equally intact seals. They probably don't and probably won't once the crankcase is pressurized.
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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
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