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Ben300SD 01-04-2001 04:06 PM

I recently purchased a 1981 300SD with 228,000 miles. When I purchased it (roughly 2000 miles ago), the engine had no problems, except for a leaky turbocharger oil hose. I replaced the turbocharger hose the day I bought the car and have not experienced any leaks since. However, my car has started to have a problem with blowby.

I took the car up in the mountains last night, and it climbed about 10 miles of a 6% grade at 70mph without needing to downshift, so I know the compression is still good. After returning from the mountains I checked the oil, and appears to be at the same level that it was at when I had the oil changed (about 600 miles ago). I also had the air filter changed at that time. Today I checked my air filter to see if it had accumlated any oil, and there were roughly two tablespoons of oil in the air cleaner housing.

My concern is how fast the blowby will worsen. Am I looking at replacing the engine in the near future, or is this something that I can drive with for a long time. Additionally, how should I drive the car to prevent the blowby from worsening? Any help would be greatly appreciated. Thanks.

IMUL 01-04-2001 06:41 PM

Another Consideration
I found oil in the air filter housing in my 240 about a year ago & assumed that it was a severe blow-by problem. Luckily, the problem turned out to be the vacuum pump. It was blowing oil through the hose that runs from the pump to the top of the housing. I'm not sure if your 1981 has this hose . My 1982 SD doesn't ... it has the single hose pump. I paid $8.00 for the pump rebuild kit. But, I found a single hose pump from a 300d at my local salvage yard for $5.00 (price included the compatible air filter housing).

LarryBible 01-04-2001 08:11 PM

I think you just gave it a good workout. When I workout, I sweat, then I get drier. In your cars case you need to give the air cleaner a little help and wipe the sweat from its brow(air cleaner).

Just change oil and filter often and keep giving this car some care. On a diesel engine, when it gets tired it doesn't foul spark plugs or burn valves. As long as you can start it and carry enough oil to get where you're going, you're in good shape.

Using a universal grade oil won't hurt either, there are extra additives especially for diesel engines to disperse soot and keep the engine cleaner inside.

Change oil hot and change oil often,

Ben300SD 01-04-2001 11:58 PM

Thank you for your responses. I have one more question, if somebody has the time to answer. While my engine doesn't have 300k or 400k miles on it, it definitely has a high amount (228k). Incidently, I am not surprised that it has a problem or two. What I would like to know is what specifically causes blowby? And what will cause it to worsen?

Mike Michalek 01-05-2001 01:30 AM


Blowby is combustion gases that gets forced by the piston rings into the crankcase. Then gets mixed into the combustion chambers.

It's evident by blue smoke coming out of the exhaust pipe when you start the car up after it's been sitting for a while. As the problem worsens you will start to notice the blue smoke whenever you come to a stop and accelerate again. When it's real bad the smoke will be pretty much constant all the time.

It's oil that can be leaking past worn piston rings/cylinders/valve guides/valve stem seals. There are tests that can be performed to locate the problem. If left unchecked it will eventually do damage to the engine.

LarryBible 01-05-2001 06:33 AM


I've enjoyed your posts. I'm sorry but I respectfully am not buying into what you're saying. Maybe it's just a misunderstanding of terminology or something.

If there is blowby, there is wear. Your explanation of blowby is correct and right on the money, but worn valves or guides really have nothing to do with blowby. They CAN be the cause of excessive oil consumption, and on these engines they most commonly are the cause. But, blowby is as you say, compression getting past the rings and into the crankcase. In Ben300SD's case, the oil in the air cleaner is most likely from blowby which would be rings not sealing absolutely perfectly.

Where I am respectfully disagreeing is that if there is wear in the engine, and who wouldn't expect at least a little wear at over 200K miles, the DAMAGE(or more correctly normal wear of the engine) is already done. The engine may not be in new condition any longer, but as long as you keep oil in the engine, the blowby itself will not cause further problems throughout the engines natural, albeit twilight, life.

If this were a gas engine, you may be fouling spark plugs which would REQUIRE correction. But with a diesel, you can keep oil in it and keep driving it with really no down side.

The good news for Ben300SD is that he indicated that it had used NO oil for 600 miles. He pushed it up the hill having a little fun and it puked a little oil in the air cleaner. Relatively speaking and considering the mileage on this engine, it appears to me that if it is properly maintained it has MANY miles left in it.

Thanks Mike,

jonvee 01-05-2001 08:45 AM

I have an 82 300SD. One "upgrade" you might consider is to replace the hose/pipe that runs from the valve cover to the air cleaner. The later ones have baffles inside to reduce the oil that makes it's way to the air cleaner. Not sure of the part number but my son's 85 300SD has the later style.


Mike Michalek 01-07-2001 09:57 AM


Thanks for your comments. Your ability of wording your reply posts I would always take respectivefully.

My response was to Bens questions at the end of his second post. I also was answering in general and not really pertaining to his problem in his first post.

I was assumeing in my response that the engine was worn and with high mileage. My understanding is that if the rings and cylinders are OK and the valve guide or valve stem seal were bad. Oil would leak into the cylinder. This would be evident at start up with blue smoke coming from the exhaust.
Let's assume the problem does not get corrected and the car continues to be driven this way for long period of time. The leak would worsen in time. Carbon deposits can eventually build up on the valves and cause compression leaks. Also they can form a ridge on top of the cylinder. After certain amount of build up the carbon can flake off into the cylinders and work its way between the rings and cylinder walls and scourge them. Allowing gases to get past the rings. The problem would just compound. This could also happen on a newer engine due to bad parts or parts being installed wrong. Off course this would not be normal.

Thanks Again

LarryBible 01-07-2001 01:45 PM


Thanks for clarifying for me.

What you are saying would certainly be true in a gasoline engine. However, a diesel engine does not produce carbon. The closest it gets is an oily goo. It's certainly not a good thing, but if the tired diesel engine sees oil changes and proper maintenance, you can typically run the engine as long as it has enough compression to start and you can carry enough oil to get where you're going. As a matter of fact, the oil that does make it past the rings or valve guides acts as expensive fuel. In a gasoline engine the oil would be fouling spark plugs and making other attacks.

I am not proposing that running it to it's complete death is a good thing, but it really doesn't hurt anything.

Have a great day,

longston 01-07-2001 02:36 PM

Am I misinformed?
I was told by my local independent MB garage that there is an "air filter oil drain hose" on my car that was improperly attached, and needed to be corrected. When I asked about why there would be such a thing, I was told that oil is supposed to accumulate in the air cleaner, that it was just the way that the system worked, and that is why there is a drain hose to return it to the engine.

patsy 01-07-2001 06:53 PM

Please disregard this post, I seemed to have confused the trap oxidizer for the oil accumulator, my car has neither. Thanks Larry for straightening out my confusion.

"Humor is the greatest protector"

[Edited by patsy on 01-08-2001 at 10:26 AM]

LarryBible 01-08-2001 08:34 AM


There is an "oil accumulator" in the air cleaner, but the air cleaner is not supposed to accumulate oil. The five cylinders will accumulate more oil in the air cleaner as blowby increases. A really tired engine will soak an air filter element very quickly and will also put a puddle on the garage floor every time the engine is shut down. I have been told that these will puddle on the floor when new, but I never bought one of those cars new.

If it is a small amount, I would suggest maintaining the engine and enjoy.

BTW, This has nothing to do with the Trap Oxidizer.

Good luck,
Change oil hot and change oil often,

Ben300SD 01-08-2001 01:53 PM

Thank you for your detailed replies. They are truly helpful. My engine does create small "puddles" of oil, but usually only after a long and high speed drive (>20 miles at >65 mph). I have noticed oil on my engine block on the side with the turbocharger. I have had the oil hoses for the turbo replaced, but the leaks continue. Do you know where these engines like to leak?

longston 01-08-2001 02:03 PM

Blow-By Normal...
My mechanic reminds me (after I read him this entire thread), that diesels naturally produce more blow-by than gas engines do, and that all engines have some degree of blow-by.

My mechanic agrees with Larry's surmise, but adds that there is a reason that the car has an oil accumulator...

In my case, @ 208K, we're talkin' about a couple of tablespoons (max) between oil changes. My mechanic thinks that is quite good for an engine with as many miles as mine has. I get some spots, but never puddles.

Ben, you might want to check to see if you have all three of the bolts under the air filter. Mine was leaking the "accumulation" because one was missing, and there was a hole there where the bolt was supposed to be. You might also want to remove the air cleaner assembly and check to see if the drain hose from the air cleaner is properly attached.

[Edited by longston on 01-08-2001 at 02:15 PM]

240Joe 01-08-2001 08:07 PM

Diesel longevity
I couldn't agree with Larry Bible more. To me, the beauty of the diesel engine is that it continues to run past the point where gas engines are sitting in the junk yards awaiting the crusher. If your diesel engine is starting ok, and isn't producing blue smoke all the time, then you can continue to run them, if you can keep oil in them. So what if they consume a bit of oil. I know people that put a quart of oil in every other tank of diesel to "lubricate" the pump and top side of the engine.

My personal experience includes completely "using up" two vehicles that went to the yard because of excessive oil consumption fouling out plugs...just as Larry speaks. I would constantly be pulling the back two spark plugs out of my chevelle 302 V8 every w/e to unfoul them. Running on 6 instead of 8 is a problem. My 81 toyota had a similar problem of oil consumption that lead to fowled plugs. If both of them were diesel engines they would have continued to function for quite a while.

I also have experience with farm tractors...and the story is the same. The diesels will use more oil (more expensive larry puts it) but their fuel efficiency and longevity of engine life beat the gas engine all over the field.

Lets see if I can get it right....change your oil hot, and change it often. And if you have an old diesel, pop the hood and check the oil once a week.

And for all those environmentalists out there, you'll never convice me that taking a car off the road because it uses a quart of oil every 500 or 1000 miles is better for the enviroment than putting 4000 pounds of junk in a scrap yard, and then going out and buying a new 3000 pounds of metal, glass, rubber, and plastic, only to repeat in 10 years. Come on people....THINK.

Motor on.

[Edited by 240Joe on 01-08-2001 at 08:18 PM]

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