Clouds of smoke.

[simon_wall69]

Got my w124 running quite well now apart from one thing.

When slowing down without using the brake, then quite a substantial amount of smoke comes out of the exhaust. This only happens when you come off the throttle and between 50 and 60mph; it is worse with the cruise control on (e.g. when going down a hill). Otherwise it's fine; car pulls exactly as it should.

A quick Italian tune up stops it happening for a period but then the problem returns in a couple of hundred miles.

 

[Xtractorfan]

First thots would be valve stem oil seals, but Im sure someone on here will have had the symptons and the T shirt....for that model..

 

[roofless]

First thots would be valve stem oil seals, but Im sure someone on here will have had the symptons and the T shirt....for that model..

think the same or piston rings worn but as it's a diesel it could be a over fueling prob

 

[simon_wall69]

think the same or piston rings worn but as it's a diesel it could be a over fueling prob

Would valve stem oil seals not manifest itself when cold? I had thought this.

I don't think it's piston rings either because the car uses no oil.

 

[television]

With a petrol engine, when the piston rings are worn it will smoke when accelerating. When the valves guides are worn it will smoke after say standing at traffic lights when you pull away and then clear for the best part.

A simple test with a compression gauge is, take out the plugs, take a reading, squirt some oil down the plug hole, if the compression comes up then its rings / bores, if nothing happens its valves

 

[Number_Cruncher]

As a temporary test, it might be worth temporarily disabling EGR. Removing and plugging the vac pipe from the actuater will do it.

On a diesel, there's no inlet manifold vacuum, so, the usual petrol engine diagnostics don't fully apply.

 

[roofless]

Would valve stem oil seals not manifest itself when cold? I had thought this.

I don't think it's piston rings either because the car uses no oil.

i can only go by the info in your first post not knowing your car so just general points so the more info you can give the better & i hope you get sorted asap

 

[Xtractorfan]

Valve stem oil seals will leak oil into the piston chamber, most noticable when the car is on the overrun downhill then when the accelerator pedal is applied the engine will burn oil and create lots of smoke..worn rings will tend to burn oil all the time and especially when the accelerator pedal is floored... no doubt on diesels other things like overfuelling..as roofless points out ..will cause smoking ..

 

[Bolide]

What engine? 606 or 603? Turbo? LHD?

(I'm sure I've asked this before...)

Nick Froome
www.w124.co.uk

 

[hairyg]

Another possibility to consider, perhaps, is the ATF level in the gearbox. If over-filled it will sometimes overflow onto the exhaust causing large amounts of white smoke.

It happened to me with my C200 and frightened me half to death thinking I had blown something expensive in the engine!

 

[simon_wall69]

Sorry for lack of details.

Mileage is 180,000; fsh. Engine is multivalve and it is rhd. atf is fine and nice and pink.

 

[simon_wall69]

What engine? 606 or 603? Turbo? LHD?

(I'm sure I've asked this before...)

Nick Froome
www.w124.co.uk

Yes, you have; you have given me a huge amount of help in the past! Non-turbo, rhd and 606

 

[simon_wall69]

Is there any way of checking the oil seals? Must be a big job to change them.

 

[Number_Cruncher]

I don't see this being valve stem oils seals - being a diesel, there is *no* inlet manifold vacuum, and the usual petrol engine diagnosis method for valve stem oil seals simply doesn't apply.

I would be much more inclined to look for the EGR valve sticking open - the crankcase ventilation system blocked or gunged up - or the inlet manifold furred up with combined EGR and crankcase fumes.

What colour is the smoke? black?, blue?, white?

 

[simon_wall69]

Black.

I don't think its valve stem oil seals either because the car does not smoke on start up.

I like the EGR valve sticking open: that does sound more likely. Last time it was off, I noticed the manifold had a lot of carbon build upon.

 

[Number_Cruncher]

>>Black.

Yes, that fits, look very carefully at the EGR.

As a temporary measure, for test purposes mind!, I disconnected and disabled the vacuum supply to the EGR on my E300D. One day,... I might get round to re-enabling it again.

Temporarily blocking the vacuum won't help you if the valve itself is sticking open - installing a temporary sheet metal blanking gasket between the EGR valve and the intake pipe would help you diagnose the problem though.

 

[simon_wall69]

Thanks for the help. That does sound to fit the problem much more and explains why the problem only happens at certain speeds. Should be quite an easy thing to try and fix as well.

 

[Number_Cruncher]

How can there be no inlet manifold vacuum when the pistons are on the downward induction stroke ?

It's because there's no throttle plate** to cause a restriction like on a petrol engine. This is one of the reasons why diesels are more economical than petrols at part load - no power is wasted dragging air past a partially closed throttle.

** Yes, there is a device that looks like a throttle on a naturally aspirated OM606, to help draw EGR into the inlet manifold under certain operating conditions, but, it can't go anywhere near being fully closed, and doesn't cause significant vacuum.

In pedantic terms, yes, the absolute pressure in the diesel engine's manifold must be lower than atmospheric for air to flow, but, this pressure difference is tiny - not even measurable with an automotive vacuum gauge. Whereas, on a petrol engine, when the throttle is closed on overrum, you can get significant levels of vacuum ~25 inHg, which will readily suck oil past the valve stem oil seals and guides.

There are/were some (older) diesels with a throttle plate which did create manifold vacuum - these were used to provide signals for pneumatic governors fitted to the injector pump. Thankfully, these monstrosities are of historic interest only!

EDIT: I've thought of a much more direct and striking way to say this - you can run an OM606 without the inlet manifold, and it runs well - you can't do that with a petrol engine!

 

[simon_wall69]

You need to remove the head, then the valves, check for valve stem wear, if no wear, grind in the valves with grinding paste, clean off, fit new valve seals, rebuild. Not a job for you if you have no mechanical tear down rebuild knowledge or the required tools. Job for an indie.

Again, this only applies if the valve seals are the cause. At this mileage, a decoke is in the timeframe anyway.

I assumed this would be the case. And no I don't fancy doing a head off job on this engine.

I will start by looking at the egr first, the manifold of the car is full of carbon, so cleaning this and the egr, etc will do some good anyway.

Surely if it were valve stem oil seals I would get oil being burned when it is started? And the car would use oil, which it doesn't.

 

[Number_Cruncher]

Taking the head off isn't easy, and it's likely to become a very expensive job. With these engines, once they've done some miles, you're quite likely to find serious inlet valve seat recession on the rearmost couple of cylinders.

To repair this, you can have new seats pressed in and machined to suit the valves - which of course is much cheaper than a new head!

When I did mine, machining, new glow plugs, new inlet valves, new upper chain guide, and other parts, the cost was over £500. I shudder to think what a garage would charge for labour for such work.