I'm still scratching my head on this one.

The transmission fluid contamination seems plausible, and I did have a trans fault code when I had the car scanned @ MB.

I had my tech check the vaccum line last year when the problem 1st surfaced and he reported that it was "bone dry"; but perhaps it just sucks it clean, and leaves no traces?

Can anyone identify the vaccum line and its location?

I'm thinking I may use a temporary block on the line and see if the contamination problem subsides.

Still working on it, but I'm driving it now, so I'm more in-tune with the car.

I've established a few ideas-

Engine is good; when not smoking it passes local Memphis emissions test -
Yesterday @ the inspection station, vehicle was well below CO and hydrocarbon limits.

After driving 30 minutes, smoke begins, along with a slight misfire accross the board (all cylinders), then oil (or contaminate is burned off and engine runs perfectly again).

Keep in mind, I took both heads off, had them machined, replaced all 48 valve stem seals and every gasket on the top end. Also new plugs, wires, and distributors.

When the car is in a smoking fit, it emits whitish , steamyish smoke that rolls like fog. Smoke is not sweet like antifreeze and coolant level has not changed, car doesn't overheat.

I noticed a wet residue running through the crankcase vent tube @ the left (passenger) valve cover when the car was smoking.

A tech @ the local dealer suggested the check valve on the oil pump being bad and the pressure being too high?

Car has had new throttle actuators and was serviced @ plaza, though the shop forman didn't remember the car and wouldn't help me with any clues...

This is something I've a little experience with as I have dealt with bad vacuum modulators beginning with my first,a '63 Mercury Meteor.

Tranny fluid is almost pure white and very acrid when it burns,that's one clue.
Also dependant upon the inside diameter of the line the smoke will be either greater or less.

Additionally in certain speed ranges and shift positions you will be able to tell when it will happen,while in drive the tranny may have greater pressure thus seeming to make more smoke.

I do not know where the modulator is on your car but the very fact you have fluid in your vacuum lines would incline me to look there first,unfortunately some Mercedes,notably my '98 did away with a tranny dip stick,how about yours?

Ohh,has the brake fluid gone down?

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Sure sounds like the engine is sucking in something that's not supposed to be there. Tranny fluid will definitely burn white, and look like fog out the tail pipe depending on how much is being burnt. It is surprising how much moisture rides along with oil vapor in the crankcase ventilation system.

First thing I would try is getting the engine up to temperature and smoking, then remove the oil fill cap (place a rag over the hole if necessary) and see if it makes a differenece. You may have to wait a bit for any moisture in the system to burn out of the exhaust. It should be possible to remove suspect hoses and lines (plugging where necessary) to see if you can isolate where the fluid is coming from.

Just throwing out a wag, but what about a stuck EGR?

My friends M120 had one of the EGR's stick open. Car had a slight miss, and smoked a bit on start up. Smelled like a carb running rich actualy.

Luckly the problem was caught and correct fast, so the cats were not hurt, ouch they are pricey!

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I have an identical issue with my 94 sl-600. Haven't found the cause -yet. It DEFINITELY is engine oil 'pooling' in the intake manifold runner. How it gets there is the mystery. I SUSPECT the oil drain-back holes on the head are marginal or? and the PCV system sucks up a little bit somehow. I am gonna modify the PCV inlet with a deflector or ?
Exactly the same symptoms 20-30 min of operation, smoke starts, then will go away. Sometime worse than others. Seems is gets a slug. Engine operation conditions do not seem to make any difference.

I agree with the brake fluid. Although I am not sure about the brake booster setup on those cars.

....Very typical on older ford and gm vehicles....Leaking Transmission modulator smokes more when you decelerate ...high vacuum....
No doubt its got a drinking problem
Drinking and Driving……
No respect for the law…..
sounds like transmission fluid. Transmission fluid smokes like crazy and you only need a small amount
May be a little experiment here Dr Frankenstein…..
Can you put some transmission fluid in a spray or squeeze bottle..
Rev it up slightly and bottle feed it with a quick squirt…..
You should get the same effect….SMOKE
Does it look and smell the same....??
Don’t try it with brake fluid!!
You can however remove the master cylinder and look behind the master and look into the booster.
Is it wet???

Try this. http://v12uberalles.com/

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Auto Zentral Ltd.

Oh, I remember a thread on this problem... There was another V12 with the same problem. It turned out to be a vacuum line leading into the throttle body that was injecting motor oil into the intake. I will see if I can dig up the thread...

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-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.

It would be GREAT if you could find that thread!!!

As an experiment , I removed the vacuum line from the trans to the intake (@the intake) , drove the car; still smoked after about 30 mins...

Now I'm guessing its either brake fluid , or oil .

Any ideas on what else I could disconnect?

is the white smoke coming out of the exhaust or just out the back of the car?have you considered an overful transmission?when the tranny heats up after driving excess tranny fluid can spill out the vent and hit the exhaust.

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon

Here's what you really need to do.

#1 Stop tinkering with the car! You probably doing more damage than good!
#2 Locate and talk to someone who has specific Mercedes Benz training on the car. Not just "some guy" that has worked on a couple of them. Make sure they have gone to the factory class! You may even have to go to a dealership to find this person.
#3 Tow the car to their shop
#4 Pay them well for correctly diagnosing your car and repairing it and preventing further damage from people who don't know what they are doing working on it.
#5 Continue to bring the car to them and have them care for it.

You notice all the V12 badges on the inside of your car and how it has a leather dashboard and other things a regular S class does not? Thats a polite hint from Mercedes that this car is not like any of their other cars and is "special" and requires specific knowledge to correctly service and repair. As much as I would love to have a V12 (more really for the interior than anything else) I would want to locate a mechanic that has worked on these cars before I would even consider buying one.

maybe this will help.............
http://www.faqfarm.com/Q/What_can_cause_white_smoke_from_the_exhaust
You need to determin what kind of fluid this is....and go from there..

That's a great idea, except for two things. There was never a "factory class" for the M120 V-12. Also, given the rarity of these cars, finding an MB tech who has worked on more than a handful of them (not just routine service) will be very difficult.

I think you should take a closer look at the crankcase ventilation system. The entire ventilation circuit should be carefully checked. Maybe monitior manifold pressure. Is it different when the problem occurs?