How serious is blow by. I took off my oil cap while engine was running and have some amount of blowby at idle. 1982 300sd with 260,000 miles.

How serious is this problem and should I start getting worried or keep driving?

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

All cars have blowby...even new ones....the real question is do you have too much blowby?

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

wish I could offer an easy way to quantify that..http://www.peachparts.com/shopforum/showthread.php?t=118532..care to try an experiment?

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

With the engine warm and running at idle.....open the oil filler cap and raise the rpm's a little...about 1000 to 1200 rpm....If the engine is in reasonable shape, the blow by will deminish slightly.

Why ? Because this 'gas loads' the rings better.

Most blow by at higher rpm's (Besides worn rings.) is due to poor exhaust valve seals and on high mileage engines, some valve guide wear.
( Exhaust pressure increasing.)

Most blow by at 2000 rpm WOT, is due to poor intake seals.
( Turbo pressure increasing.)



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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

If your oil cap will sit on hole while engine is running and cap is not screwed on I would consider it within normal range. If it puts oil cap into low earth orbit you may want to use a straight 40 oil in engine in summer to minumise blowby to some extent and reduce oil consumption. Inside your air filter housing is also a good indicator as if not too oily an air filter or housing is certainly a good sign in my opinion.

Forget about it and keep driving. When the engine becomes hard to start then you have a problem.

Blow by tells you what you already know, you have 260k worth of wear on your engine.

The only fix is to rebuild.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I gotta agree here. As long as your engine starts easily when it's dead cold, you should be ok.

- Patrick

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1982 240D. 198k, Marine Blue/Blue, 4 Speed, Crank Windows, No Sunroof, No Rust, No Oil Leaks
2001 TDI. 197k, Lagoon Blue/Black, 5 speed, Chip, G60/VR6

hm... that reminds me, i haven't seen a fresh oil thread in a while...

There's been an opinion expressed, on more than one occasion, that certain motor oils may be of help with blowby. Searching will turn up more discussion on the subject than you'd ever want to see. Myself, having been awed at the amount of blowby my car has, I opted for 15W40 oil (dino), and it did help some.

Unless they replace worn metal in the rings and cylinder walls, no oil is going to help.

On some engines that are either not driven much or sat with old oil in them for a long time it is possible that the rings could become gunked up or stuck. Usually a high detergent oil and some hard driving will clean it out, or an additive such as "seafoam" or Marvel Mystery oil.

You could try a thicker oil like a 20w-50 or 15w-50, that may do something.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I tried Castrol 20W-50 in the winter and the car was very hard to start. I went back to 15W-40 and the car starts fine in the winter - no problems.

Thanks for the advice. I did just change brands of oil from Rotella 15W40 to the LE Monolec or Lubrication Engineers dino oil. This is supposedly the absolute best dino oil you can buy. It is a red color and is run in the million dollar diesel earth movers. I am going to experiment and see how the oil consumption drops.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

On the 300SD there was lots of oil blowing down the tube (reasonable amount) and the oil collecter was picking it up however the air that was leaving this unit was drenching my air filter in oil.
Some brake clean, clear silicone, and Avaiation Sealent (brown goo) fixed that problem right up and now my air cleaner stays as colorful as new I would just seal up your CCV system joints real well and call it good...Let the oil collection thingy in the air filter do the rest