My wife's 300TD has its vacuum pump exit hose running into the top of the air cleaner, mine does not. This would only ever be a problem where that hose feeds into the air inlet. I have never had any problems with my vacuum pump, her's has been repaired several times, always with a torn diaphram. Only once did the problem get bad enough to cause run-away.

To control it, certainly turn off the key to cut the fuel supply, but be careful not to lock the steering. The more vacuum you consume, the more the pump will operate, the more oil it will tend to pump into the air inlet; so try to reduce the vacuum used, unfortuneately that means not using the foot brakes. Of course, if you have to use them, do so, you could certainly bring the car to a halt but the engine wouldn't stop. Ideally you would have a second person pull out the vacuum line into the air cleaner before the transmission failed. Otherwise keep driving and wait for the engine oil to run out and so starve the engine of it's fuel supply. I don't imagine the lack of engine oil would cause damage because as soon as the oil pressure dropped off the engine would stop.

To avoid the problem ever happening in the first place it would just be a matter of removing the vacuum pump air exit from the air cleaner and blocking the hole. I can't see any need for that hose to feed into the air supply. Just tie down the hose and let it breathe naturally.

Thanks WHunter for putting the fear of God in me before I installed my vacuum shut off in the 300-D. We held the manual shut off in the off position for the initial installation. Then we loosend the injector lines at the injectors. I then disconnected the glow plug relay and hooked up a MityVac to the shut off. Next we turned the engine over with the starter and alternated on-off with the vacuum watching the loosend injector lines for fuel on and off. First start up was without the air cleaner on and a 1 inch pine board was handy just in case. The thing works like a champ! Thanks again.
J. R. B.

__________________
1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

Never do this:

Q: From: John Doe
I have been told to clean away sludge and buildup inside the engine to drain the oil, fill with diesel and run for a couple minutes then replace.

A: This is a great way to junk a diesel engine, for reasons explained earlier in this thread.

it's running! AWAY!! TWICE!!

It does happen to real people.

"without the air cleaner on and a 1 inch pine board was handy just in case."

Gee Whiz... we are dealing with Mercedes Benz here.... don't you have any OAK , Walnut or best of all .... Zebrano to match the interior wood ?

I hereby accept my admonishment and promise never to use a lowly pine board again. From now on it is only the best Mahogany. I can only hope that the spirits of my German ancestors will forgive me.

__________________
1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

Assuming that no work has been done on the engine or IP, and that the runaway is caused by blowby gases entering the combusion chambers via the air cleaner housing, would removing the oil filler cap tend to reduce the runaway?

As our 300Ds are RHD vehicles (in Oz), the hood release is on the passenger side of the cabin. This means it is not practical to qpen the hood to block the airflow to the negine, if travelling alone.
How would you recommend that we react to a runaway, while driving?
I considered a few steps below, have I missed anything?
* If engine has full power and releasing pressure on accelerator does not slow the engine, this may indicate engine runaway.
* Apply brakes to reduce vehicle speed.
If condition persists, continue with the following until it is stopped.
* Pull over to the kerb and stop the vehicle using the brakes.
* DO NOT PUT TRANSMISSION IN Park or Neutral.
* Turn ignition key OFF
* Apply parking brake. Slowly release service brakes to see if parking brake holds. If it holds, open hood and remove Oil filler cap. If parking brakes do not hold, use mobile phone to call someone close by to come and do this while you maintain pressure on brakes. It may be preferrable to drive to a garage to obtain assistance.
* Remove air cleaner cover and cover air intake with a solid object, block of wood, hardcover book, etc.

Any changes/additions to these steps?

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Runaway caused by blowby gases entering the combusion chambers via the air cleaner housing:
Removing the oil filler cap may reduce speed = 50/50 gamble.
The engine will be junk before you can reach any garage to obtain assistance.
Remove crank case vent tube, use a CO2 extinguisher through air intake.

I think I'm having this problem but my engine does not "runaway" I turn the key to the off position and take it out but the engine will stay on idling at the same speed as if the key was in the on position with the car in park. I haven't had a chance to start diagnosing and fixing this but is this what everyone calls a runaway diesel?

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

Not by a long shot. You likely just have a broken vacuum line to your shut-off diaphram. Here is the easy way to tell. Look under the hood for two *brown* plastic vacuum lines. One goes to firewall and the other to the injection pump on the engine. Gently pull off the line on the engine line with the key off and the engine still running (As per your problem). If it sucks on your finger you need a new shut-off diaphram. If it does not suck, look for a vacuum line disconnected somewhere in the engine compartment.

Runaway means your engine revvs to redline (5000rpm sometimes higher) and stays there uncontrolled. Thats when *you* run away and wait for the pistons to find a new home on the garage floor.

hahahaha thanks a lot for that clarification. Sounds easy enough to fix and diagnose.

__________________
W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

Very clear, direct and well stated.

Misspelled word and all.

you dont tighten your parking brake and dont angle your wheels on a hill when parking. Not trying to be a smart a___ but I saw a runaway diesel in Seattle and comically enough, the owner chasing it for a block. Luckily the car didnt hurt anyone

if it was not such a danger.
Chuckle, chuckle, ummm, thinking about it, it is funny trying to picture owner chasing the car. ROFL, :cracking up:
Thanks Carrameow, that was great!