I just heard from the shop that my '84 300D is suffering from blow by. I haven't heard yet what that means to me and my baby, though. If it were a 1965 Vespa, I'd know exactly what it means, rebore, rings, and first oversize piston and a couple hours of work. I also found oil in my air filter quite alot actually. What does it mean for a 1984 300D?
Car has 416k miles.
Thanks.

Did the cap test under the hood Here is a video https://streamable.com/3f4h3b

It means your engines old and worn. However. If that's all the blowby you have it's nothing like as bad as on the two 81 240D's I had, which both had steel oil caps which would shoot off like ricocheting bullets whenever I tried that test. Still drove each of them for five years and about 100K miles between the two of them.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

That's nothing ~ they're blowing smoke up your dress trying to cheat you for a rebuild/overhaul .

Anytime you can rev. the engine and not loose the oil cap it's great, no worries at all .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

If it starts ok cold and produces decent power forget it and drive on. Use diesel rated oil, keep it changed and push the car once it is fully warmed up to keep the rings moving and clean. Push it hard uphill and let it coast downhills.

If the oil is dirtying the air cleaner too much, add a catch can to the breather. It will keep the air cleaner, intake manifold, ports in the heads and combustion chamber while reducing the likelihood of a runaway diesel engine.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Yeah, that's not blowby! That's a decent working engine! Keep the oil changed, maybe stick some new nozzles in the injectors and have them balanced, but as it is, just drive it. If it makes good power, it'll probably outlast the wheel bearings and every piece of rubber on the car.

Phil Forrest

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1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

Looks like an example of a VERY healthy engine in my book.

I've had/been around a number of 617s (Mine and my families) that had vastly worse blowby, like others had said where it would blow the cap off, and smoked oil vapor like a chimney out the valve cover while you hunted to see how far away the cap was.
Cars still ran fine and started OK, usually needed to be plugged in when it was cold to get enough heat to fire off, but above freezing they ran flawlessly, and didn't consume an abnormal amount of oil either.

I once heard a guy who didn't know much about diesels mention that an old farm tractor was puffing smoke/oil vapor out the draft tube, which meant the engine was so worn it might blow up within half an hour if the owner kept running it.

I laughed and said don't ever look at my equipment, nor my work trucks, the telehandler spits oil drops out the draft tube. Its free rust proofing, but for an 8000+hr engine before the hourmeter quit on a piece of heavy equipment, I expect it to be a little worn.

The oil cap blowby test is barely a test of engine healty, its a very vague indicator, I'd be more inclined to take oil consumption and cold start performance as a health indicator.

If it starts good (even in cold weather), runs smooth, makes decent power and doesn't burn obscene amounts of oil, its pretty healthy in my eyes.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

You could get the Harbor Freight tester and do your own. Did the mechanic adjust the valves? Where is it leaking? How does he know?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Just out of curiosity, how much oil consumption is considered "acceptable"? This is assuming the engine doesn't leak oil or smoke excessively and also makes "decent" power.

Just me but with no obvious leaks I like to see better than 1200 miles per quart. Opinions may vary I understand.

On many of these engines if you fill the oil to the full level. They will burn some oil till you get lower on the dipstick. Is pretty well known. Filling to only halfway between the stick marks is fine as the sump holds so much oil on these engines.

In my mind/experience, I aim for 1 quart every 1000 miles as being an indicator things are ok but getting a little tired.

I drove my blue car 1500 miles on a trip back in october, and the oil level appears unchanged, I checked before we left and it was dead on the top hashmark/cutout, and after the trip, it can't be more than 1/16 of an inch below that. Very healthy in my book, sad that it got ran without oil before I got it and wiped out the cam, but with that fixed up I expect it to last many many years.

We had a 83 that had 383k on it when we pulled it out of a junkyard, they got it with a "bad transmission", the trans was empty. We filled it up with ATF, and it ran and drove, but it obviously had a very hard life.

My dad drove that car for several years, then my brother drove it for a few more, and it went through some oil, probably a quart every other tank of fuel, Likely turbo was the cause of oil consumption, as when we got the car it was a bit down on power, the turbo was siezed up solid from sitting.

Didn't smoke at all, made decent power, but wow it would not start in the cold at all unless it was plugged in.

Oil consumption isn't a definitive engine is worn out sign, but is in my mind a better indicator than the cap rattle test, as if the PCV system is working properly, most blowby will end up getting sucked into the intake/oil separator stuff. (try the cap test but stick your finger over the PCV vent to see just how much of a difference it makes)

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

Thanks for the reply. I'm rather new to this "scene" and noticed my 83 240D does just what you said. If I fill it to the top mark on the stick, it'll drop to the 1/2 qt mark fairly quickly. I guess I never waited to see how much further it would or wouldnt drop as I'd top it off. Also not sure how long time/miles it takes to drop.
Good info, good to know. Just celebrated 64 birthdays last month and have never experienced this 1/2 qt loss in the many cars and trucks of my life. They say ya learn something new every day....
Thanks!

^^^^ THIS

You're doing fine 123Boy ~

It's supposed to be fun and educational, not nerve wracking .

Do all the little maintenance things and learn the quirks inherent in any machine new or old and then go drive and enjoy it .

Don't get in a panic about the little things some will try to scare you with, these are well designed and sturdily built vehicles, the 240D in particular was the most popular taxi choice in the world when it was in production .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better