After doing a little heater hose work today, I started the car up, and it began smoking from the exhaust. This is interesting, since it didn't smoke the last time I ran it. Nice blue smoke, not tons of it, but enough to get my attention. Further investigation reveals that the car now has a steady stream of oil poring in to the intake from the crankcase vent hose. Blowby is also through the roof, where as the last time it was run, blowby was minimal. Now the cap blows off with the vent line plugged.

I'm thinking I might just cancel my wheel alignment in the morning, because something is clearly very wrong. I'm afraid it may have spontaneously cracked a ring. I guess I'll know when I get done checking compression. Any ideas as to what has happened?

Discuss.

I'm going to go kick the car a few times in disgust, then see if I can find my compression tester.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Check your vacuum pump diaphragm also.

__________________
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'm a little scattered from this, so I forgot to mention that the vacuum pump is fresh, and is working properly.

I still can't find my compression tester... It's in these boxes somewhere. I did take a couple of videos with the phone to let you all see just how bad it is.

This is the tailpipe smoke. It's easier to see at idle than you can really tell from the bad video.



And here is the vent tube dumping a lot of oil in to the intake manifold. Towards the end of the video, I reached up and loosened the oil fill cap. Without plugging the vent tube, it now dances madly. If i plug the tube, it blows the cap off completely. The last time I did this, it danced less with the vent plugged than it does now unplugged. The difference? A week and about three miles of test drives. This is sudden and severe.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Man, thats just weird, it doesn't have a major miss or anything with it?

One thing though, be VERY careful running it now and have a big thick rag handy to cork off that intake, this is exactly the makings of a runaway engine any time you try to run it right now.

__________________
Chris
64 190D R.I.P.
80 240D W/617 engine -for sale
82 240D -for sale

Well, one cylinder has lost 130 pounds of compression, and it does miss when cold. I'm guessing piston/ring failure of some kind. Adding a little oil to the cylinder brings compression way up.

I'm really too irritated at the moment to include any other details.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

It's difficult to comprehend a piston/ring failure with the vehicle sitting in the driveway.

Take it out and drive it for awhile. You won't hurt anything and the stuck ring might just seat properly..........if that's your issue.

The theory that the engine can run away due to excess oil consumption is largely a myth. Once you start to fog the neighborhood and someone calls the police.........that's the point where you might consider shutting it down..........not before.

"The theory that the engine can run away due to excess oil consumption is largely a myth. "

There is a much greater chance of a diesel running away if there is a fuel leak into the crankcase and the level rise to a critical level and then bam. Ask me how I know.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Actually VW diesels in the 70s and early 80s were plagued with runaways until the engine would self destruct. There were several TSBs and breather mods to prevent it, most of which were ineffective. Also I have seen turbo diesels (Never a MB) where the turbo shaft and bushing wore enough to allow the engine to run away on motor oil. Interestingly at 65 to 75 MPH the smoke is not so noticable. Soon the engine will not slow down and then it is too late.

As for driving it to loosen a stuck ring, I highly recommend it as rings will stick when an engine sits for a period of time. An oil change before the drive would also be recommended.

__________________
Retired
ASE Master Car / Light Truck
ASE Master Medium Heavy Truck
EVT Master Technician Ambulance
EVT Master Technician Fire Apparatus

"Without Fleet The Pride Doesn't Ride"

1983 300SD 609K + still going strong!
1970 Monte Carlo
1994 Ford F150

If you look at the typical fuel consumption of a diesel engine in an automobile, you'll find that it varies between .5 and 4 gallons per hour depending on the load. This is for a typical 3L engine.

If an engine suffers from serious oil consumption and consumes one quart of oil every 100 miles the consumption per hour is still less than .12 gallons per hour. It would be impossible for such an engine to runaway on oil.

Now, if you wish to make a case for oil consumption in the range of one quart every 25 miles, you would be in the situation of fogging the neighborhood and potentially risking a visit from the police as I mentioned above. This is the point to consider shutting it down.

Therefore, my original advice stands.

I respect your input and in theory it is sound, Having seen many of your posts in the past I do respect your experience and opinions. However after seeing this happen more than once, I know it happens. The oil from the breather usually is in spurts, it tends to accumulate then dump into the intake which causes the engine to accererate, which produces more blowby, which pushes more oil and so on. Like I said it is not much of a problem with today's diesels as in the past. Also it doesn't happen driving around town, almost always on a long, highway speed, drive. I have been a professional diesel mechanic (rebuilt my first 190D in 1971) all my adult life and I have probably seen 20 engines that ran away from oil ingestion, but never a Benz. I have never personally driven a runaway, but have spoke with those who have and it is a little un-nerving when at 75mph to take your foot off the throttle pedal and the vehicle continues at speed, then slowly accelerates, turn the ignition off and it still goes faster until the rods stretch and the pistons hit the cylinder head bending the valves. This is the usual scenario. But I also rememeber a tear down on one that had the wrist pin broke on a runaway and the rod went through the side of the block. Of course all the owners claimed that these, now failed engines, did not use much oil.

What I did find puzzling is that the pistons would always hit the head before the crankcase was empty and damage the bearings or sieze up due to a lack of oil pressure. One VW Rabbit owner claimed his was nearing 100 MPH with the switch off and his foot on the brake when it broke!

__________________
Retired
ASE Master Car / Light Truck
ASE Master Medium Heavy Truck
EVT Master Technician Ambulance
EVT Master Technician Fire Apparatus

"Without Fleet The Pride Doesn't Ride"

1983 300SD 609K + still going strong!
1970 Monte Carlo
1994 Ford F150

I don't disagree that it can happen. However, in all cases, I believe you'll find a catastropic failure of an oil line or a seal where a huge quantity of oil can be ingested by the engine in a short period of time. Oil consumption in the range of two quarts per hour would be necessary for such a event to occur. Even two quarts per hour is insufficient for a runaway if the engine is under load.

In the case of typical blowby..........even if it's considered massive blowby.........the engine is nowhere near the level required for a runaway.

I sense an experiment in the works. Anyone got an old engine they don't care about? Start it up, let it idle and slowly feed oil into the intake while measuring the amount.
Couldn't be any worse than the YouTube video where they ran the MB engine wide open no load until it failed.

__________________
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

You'd need a glorified eye dropper. The fuel consumption at idle is probably .5 ounces per minute. The engine will probably increase speed before this level due to the addition of the oil. I'm guessing that you could get it to run away at 2 ounces per minute. However, atomization and droplet size is also a factor.

Okay, I'm calm enough now to give more details...

I actually had the brilliant idea of running the vent hose in to a small container, about the size of a large baby food jar. With the engine idling and fully warmed, the jar was half full in about a minute. Now, I'm not inexperienced with internal combustion engines, as I was a mechanic for a few years, but that strikes me as a mechanical failure far worse than a stuck ring. Mind you, it didn't do this last week. Last week it ran perfectly.

Immediately prior to the great smoke issue rearing it's ugly head, I heard a bizarre noise from the engine during the first start attempt. (This thing always takes too attempts to start cold.) It was an odd sound that I can't even begin to describe, but it had a definite clank to it, almost as if the engine fired backwards once as it was beginning to come to life while the starter was still engaged.

I honestly think something may have broken when that happened. Cylinder three has lost a lot of compression, and I've also noticed that the starter cranks slower now, amd there is a faint scraping sound at start-up. I've tried making an audio recording, but the mic in my phone just isn't that great.

I'm thinking that I'll call this motor dead for now. I don't have a shop to work in, so I have no place to even begin tearing down the motor. As luck would have it, I located an '82 with the turbo motor at a salvage yard about twenty minutes away from the car. It has 240K on the clock, but they say it runs well, and the motor is still in the car, so seeing and hearing it run would be possible. They want less than $500 for it, and to be honest, I think the cost to repair my current motor might easily exceed that. Exhaust system changes and larger radiator for the N/A to turbo swap aside, it seems like an ideal solution to me.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Damned glad to hear there's still original Stuttgart built 617 replacement engines kickin around at junkyards. Yer brand new 240k mile engine is better than rebuild says me. Could need timing chain as I'm sure y'all know, otherwise plug'n play.

Meanwhile please pull cyl head if you've got time after engine swap, Mr. KAdams. Or at least check valve train and return to this thread. Those of us planning to rack the same 1/2 million miles gotta know what killed it. And high mileage threads like this serve the community at anticipatin problems best.

My guess is bent stem eaten valve punched hole in piston crown. D'you know if valve job with fresh guides was done, say at 300-350k miles or so? Brand new 116 300SD of mine has 262k. Am planning on doing new head gasket and valve work in another couple years myself. And any feedback in this regard is much appreciated.