82 300SD with 140K miles. Does anyone know the reasons for heavy blowby and what to do about it? Rich

Caused by poor engine maintenance, such as infrequent oil changes, or extra wear caused by combustion chamber coking from continued use of poor fuel.

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

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

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

Compression rings wear from age, poor oil quality (Old oil), and normal wear and tear. As they wear, air during compression and power strokes leak past the rings, through the crankcase and out the breather tube. All engines (even 0 mile 2007 engines) have blow-by.

The only true fix for blow-by is to rebuild the engine. However, a ring job can be a sub-$2000 way to get by for a while.

Unless you have starting/running problems from low compression, blow-by is little to be worried about.

Start by defining "heavy." The standard test, which you may know, involves pulling the crankcase breather hose off of the air filter or wherever it goes in your model and plugging it with your hand (wearing a rubber glove so you won't get oil all over you). Wait until the engine stalls due to the pressure buildup. If it stalls in less than five seconds, that is excessive blowby. If the pressure is so great you can't keep the hose closed, ditto.

Blowby is primarily due to combustion gases getting past the rings and into the crankcase. It can also be caused by worn valve guides. Either way, it is a form of pollution, which is bad, causes excessive oil use, and means expensive work. As my experience with such things is limited to gas engines, we need someone with more diesel experience to step in, but it sounds like your engine needs guides or rings or both, due, as Pete says, to lack of proper maintenance by a PO.

Additional tests (compression, etc.) will help pinpoint the cause more closely. Depending on the condition of the vehicle otherwise, you may have to make a decision. Many people believe that, if a major component is lost, the vehicle should be replaced. Clearly, that is a personal call on your part, but it is certainly true that the value of a rebuilt engine or transmission, plus labor to R&R, is probably more than the value of the vehicle. If you can do the work yourself, have a donor car, etc., that is another thing, but if that were the case you probably would not be asking the question that you did.

If you can provide some additional information (how does the vehicle drive, does it start easily, fuel economy, condition otherwise, etc.) the forum may be able to offer additional advice.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If you perform that "standard test" and you blow out the crankshaft seals in the process..........let it be known that you have been warned.

If I had a potential buyer do that "standard test" to my car, well, lets just say it would be the last time they see my car.

Aside from the "test," the question is, what does the OP mean by "heavy blowby"? Is this a judgement based on removing the oil cap and seeing lots of vapor, is it based on a mess on the valve cover? The blowby shouldn't be to bad with 140K miles, should it?

The blowby could be horrible if it had two oil changes in 140K.

But, blowby is a very subjective thing and persons unfamiliar with diesels can surely mistake typical blowby with "heavy blowby".

That's really what I'm wondering, especially if the cap or the breather hose are leaking, a little blowby can make a huge mess.

It's kinda hard to describe something like blowby on a forum. The only way to help people understand what kinda blowby you have, would be to take off your oil cap on the valve cover and set it back on the hole. If it blows it out of your hand, thats a lot of blowby . If it just kinda dances around or sits there, thats fairly normal.

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"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

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