I am getting a good bit of blowby now....I can really see it when I remove the oil filler cap. Is this normal for a turbo diesel with 200K+ miles? Is there anything I can do to reduce it?
Thanks

Do a search on blowby and you will find a number of discussions on this topic. At one time I suggested a scientific comparison utilizing garbage bags placed over the oil fill hole, timed to see how long they fill.
It is nothing to worry about as long as the engine starts and runs well.

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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

I agree with Kerry. Although it is a sign of a worn engine, one of the beauties of a diesel engine is that if it will start and you can carry enough oil with you to get where you're going, you can still drive it.

This is not true with a gas engine because when they start getting worn, they will foul spark plugs and other ills.

Keep it full of oil and enjoy.

Have a great day,

Thanks for the info...I feel better now.

I have an old 78 300D with 352,000 miles. It has had noticable blowby for the last 100,000k miles. So long as I keep it under 60 mph it does burn that much oil. I did find that using the proper diesel rated oils slows the oil consumption. (DELO) .
Doesn't seem to get any worse. I have read here that the pistons on these old diesels are likely to wear the cylinders oval.
Have a much lower mileage 300D engine and trans sitting in my garage, hope to install them later this year. But until then I just check the oil weekly and add a little as needed.

Good pistons are not generally made round. They are made oval due to the difference in the expansion rate between the direction that the wrist pin is and 90 degrees to that...
If one put in a round piston, and it expanded normally it might wear an oval pattern in the bore....
Or someone might have measured a piston and found it was oval , not knowing it was intentional, and assumed something from it...

Thank you Leathermang, I believe the correct answer was that the holes are prone to wear oval, not the pistons, which are manufactured oval. Seems these engines hold up well enough anyway. I mean not many 350K mile engines that are still intact, much less that will start everyday.
And no tune ups either!

I've got quite a bit of blowby on my engine. In fact, I was scared by the blowby enough that I came within a split second decision of not buying my car, particularly because the last time I saw blowby that serious, it was due to a cracked piston, and that I had a 2000 or so mile trip ahead of me (east Texas to northern California).

However, I decided to take a chance, because the car started and seemed to have good power. I drove it down to Austin, where two board members on here were gracious enough to run a compression check for me, and the car passed with flying colors. I also haven't burned any noticeable oil since I've had the car (I've lost a little bit, but I think I have a leak somewhere as I've seen oil towards the back of the engine, I lose less than a quart every 3000 miles, so I haven't really tried to look for it ).

The car had about 223 or 224K miles on it when I bought it; I've got 236 or 237K miles on it now, with no engine trouble whatsoever. Stil starts nice and quick, has good power, and I'm happy.

So, in essence, it would be a good idea to run a compression check, and to otherwise keep on driving.

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

Is it hard to run compression tests? I'm curious what my mercedes compression is like, and it'd also be helpful to do on my MG. Thanks for the info.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

If you have a tester and a helper, it's pretty easy...TXBill used the injector holes on my car, so he pulled the lines and each injector one at a time, and had me crank while he read the gauge. I think he let it go for 3 or 4 compression strokes.

After seeing him do it, I think I could do it myself, if I had a gauge...

__________________
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

Blowby is combustion gas leaking by the compression rings. If you have a lot of "smoke" comming from the oil filler cap, it's can be bad proportional to the amount. An engine, gas or diesel, when put under power, has more combustion chamber pressure, and will produce more blowby than setting at idle. While it's hard to say what's to much, it is safe to say that if your going to work an engine, that is pull trailers or drive up long steep hills, you are at risk of burning the ring lands off a piston and having an engine failure. The next time you do that blowby test at the oil filler cap, have someone go put the car in drive and powerbrake it compair that blowby to the no-power test. Also, if blowby is a smooth flow, it's telling you that all the rings are worn a little. If you see intermitent (puffs) it means you may have a broken ring or damaged piston. Also, I do a quick comp. test by holding the fuel stop to off while having someone crank (start) the car. If I hear an even, consistent sound as the engine turns over, it's a sign the cyl's are of equal compression. If every 5th has a free sound, i'm looking for a compression issue, either valve or piston/rings. Hope this helps

Can you expand on that a little?

Also with compression testing, is the guage specific to Mercedes? My husband read in the Haynes manual something about Mercedes renting equipment? Is that true?

Natalie

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Natalie

The smoke from the oil filler cap can tell you alot, but puffs and streams really mean nothing. LarryBible the diesel guru says that oil droplets coming out of the filler cap must be there, or the cam is not being lubricated! If it runs well, starts well, has good power, and has all of these consistently, then you can say your engine is good. People tell me my overanalyzation is bad. Little things like engine noises, blowby etc can drive you insane. If it runs good, it probably is good!

I have a compression tester with adaptors for most engines. This tool is basic, and only needs to check pressure. As for the listen-as-I-crank method--- On any given engine, I do whatever it takes to not have the engine start while I crank it. On a gaser I unhook the power to the ingition. On a diesel I stop the fuel, even if it means loosening the lines to all the injectors so they can't get fuel. Then, crank the engine and listen. As each piston comes up on compression in succession you will hear it as the compression slows the crank speed a little. If this sound is the same throughout perhaps 4 or 6 turns of the engine (2 or 3 complete cycles) than the compressioin is uniformand and all cyls. are the same. This doesn't mean they are good enough. In most cases if the engine starts ok, than the compression is at least ok for moderate driving needs. If however while cranking you hear a periodic change in sound (if the starter seems to speed up perhaps every 5th compression stroke) this indicates extremely low compression on one cylinder. Sometimes a valve adjustment will restore compression. Sometimes they need a valve job. Other times If you see large puffs of smoke at the oil filler cap (cap removed) all of that compression could be passing by a piston. If this helps a little, but...... get back to me at gbkramer2000@yahoo.com