Choked inlet manifold on ML270

[Alex Crow]

... i thought we started with "my manifold is full of gunk - how about a way of preventing it?"

egr is an abomination, but it is there as one of the best compromise ways of reducing NOx emissions. there are other systems being used such as aftertreatment with urea, and throttled intakes to reduce compression - yes, i have been googling - but there is no ideal solution that ticks all the boxes yet.

there is an argument to suggest that egr is "unenviromental" due to net effects of increase of other pollutants, increased fuel consumption, and of course extra energy used in production. arguments can also be used for catalytic convertors being similarly misguided - production of the precious metals needed causing significant CO2 emissions etc.

 

[dieselman]

... i thought we started with "my manifold is full of gunk - how about a way of preventing it?"

That black gunk is the particulates being recirculated though.

I agree about the over complicated emission systems for diesel engines. My belief is that they should be made to produce maximum mileage and minimum Co2 and not worry about anything other than soot, because they are producing such a small volume of pollutants anyway.

 

[Number_Cruncher]

I think we may have been perilously close to a real solution to the problem with DM's suggestion of changing the inlet manifold gasket.

The processes which lead to deposit formation are extremely temperature critical, and it may be the case that Oigle's car has higher underbonnet temperatures than we usually see in the UK. Simple modifications which cool the manifold might be enough on their own to stop the problem.

 

[oigle]

I think we may have been perilously close to a real solution to the problem with DM's suggestion of changing the inlet manifold gasket.

The processes which lead to deposit formation are extremely temperature critical, and it may be the case that Oigle's car has higher underbonnet temperatures than we usually see in the UK. Simple modifications which cool the manifold might be enough on their own to stop the problem.

My car certainly has higher underbonnet temps, mainly due to the fact I do a lot of towing and often see water temps approaching 100 degrees C. Of course, our climate tends that way too.
If I was to start all over again, I think I would leave the EGR alone and concentrate on removing the oil from the inlet system - re-route the PCV away from the inlet and use flame arrestors and a high mounted catch bottle that could drain back when the engine stops. Much easier to setup.
Without the oil in the manifold, the dry exhaust soot should pass through the EGR and manifold without sticking anywhere - just like looking at the end of the exhaust pipe. Simpler solution, me thinks.

 

[Number_Cruncher]

>>concentrate on removing the oil from the inlet system - re-route the PCV away from the inlet

That isn't a route that would tempt me - the inlet valve seats on diesels see very little oil, and the PCV represents the best source of lubrication for the valve rim and seat. Although I'm usually anti-modification, my EGR is blocked off!, (for test purposes!), but, of course, my car doesn't monitor inlet flow, and there's no possibility of fault codes being set.

 

[Wirral_guy]

Before I add my bit, this is why I like this forum the best - extremely knowledgeable people discussing highly technical ideas and solutions in a measured and interesting thread. Admittedly, a lot of this has made my head hurt but I know a lot more about the intake of a diesel now

Getting back to the original post - Am i being stupid/missing something but couldn't you add a replaceable filter of some kind to catch the sludge buildup and stopping it fouling the rest of the intake? The only thing I can think of is that the buildup would be too rapid for the filter to last between normal service intervals.

Dave

 

[oigle]

Before I add my bit, this is why I like this forum the best - extremely knowledgeable people discussing highly technical ideas and solutions in a measured and interesting thread. Admittedly, a lot of this has made my head hurt but I know a lot more about the intake of a diesel now

Getting back to the original post - Am i being stupid/missing something but couldn't you add a replaceable filter of some kind to catch the sludge buildup and stopping it fouling the rest of the intake? The only thing I can think of is that the buildup would be too rapid for the filter to last between normal service intervals.

Dave

I wish !!!! The oil comes from the PCV inlet and the soot comes through the EGR, directly into the manifold. They mix beautifully inside the inlet manifold and form a lovely glutinous mess on the EGR and all the inner surfaces of the inlet manifold, including the swirl flaps. Some of it sets quite hard after a while and it is horrendous stuff to remove.
Better to find a preventative if possible.

 

[oigle]

>>concentrate on removing the oil from the inlet system - re-route the PCV away from the inlet

That isn't a route that would tempt me - the inlet valve seats on diesels see very little oil, and the PCV represents the best source of lubrication for the valve rim and seat. Although I'm usually anti-modification, my EGR is blocked off!, (for test purposes!), but, of course, my car doesn't monitor inlet flow, and there's no possibility of fault codes being set.

Wonder if they need the lubrication. On petrol engines, the valves etc used to rely on lead in the fuel. When unleaded came in, the seats were all hardened and were not supposed to need any lubric. Are diesel engine seats softer? I was under the impression PCV was only another antipollution measure - engines used to just have a breather back in the old days - admittedly that was when we used leaded fuels.

 

[Alex Crow]

inlet valve seat lubrication from pcv cannot be an exact science. we do see some cdi engines consuming absolutely minimal oil - perhaps as little as 250ml in 10,000 miles. assuming only a percentage of this goes through the inlet you have to wonder if it can have any bearing at all. conversely i have seen an ml270cdi that used around 1L per 1,000 miles from new! and MB would not entertain any warranty as they have official max consumption figures that are even higher!!

i accept that number cruncher does have a point, indeed on his 606 engine inlet valve seat regression is all too common, but i am merely pointing out the vagaries of this function of pcv if it is a relied upon benefit.

and dieselman, quote: "That black gunk is the particulates being recirculated though", we have definately covered this! i am not that forgetful!!

oigle makes an observation that the manifold fouling is caused by a combination of pvc and egr, i wonder if this is the case, or if the pcv has no real bearing on it at all?

to oigle: what oil consumption would you estimate for the car? - many thanks for your experimentation and thoughts so far, you have indeed provoked a most stimulating continuation of a thread.

 

[oigle]

inlet valve seat lubrication from pcv cannot be an exact science. we do see some cdi engines consuming absolutely minimal oil - perhaps as little as 250ml in 10,000 miles. assuming only a percentage of this goes through the inlet you have to wonder if it can have any bearing at all. conversely i have seen an ml270cdi that used around 1L per 1,000 miles from new! and MB would not entertain any warranty as they have official max consumption figures that are even higher!!

i accept that number cruncher does have a point, indeed on his 606 engine inlet valve seat regression is all too common, but i am merely pointing out the vagaries of this function of pcv if it is a relied upon benefit.

and dieselman, quote: "That black gunk is the particulates being recirculated though", we have definately covered this! i am not that forgetful!!

oigle makes an observation that the manifold fouling is caused by a combination of pvc and egr, i wonder if this is the case, or if the pcv has no real bearing on it at all?

to oigle: what oil consumption would you estimate for the car? - many thanks for your experimentation and thoughts so far, you have indeed provoked a most stimulating continuation of a thread.

I too am of the opinion that the amount of oil escaping through the PCV valve would not be enough to lubricate inlet valves. My vehicle normally requires about 1 litre of oil in 10000km. Question - how much is burnt normally and how much is escaping through the PCV - unknown. Also, how much is sitting in the bottom of the intercooler? I didn't clean it out.
My observation re PCV and EGR combining to form the gunk is based on appearances only. Pure diesel exhaust residue is a little greasy for sure but the buildup in the EGR and manifold over 100000km is nothing like what you see in the exhaust pipe, or, as I can now state, inside the "cooler/heater" which I have removed. The fine residue in both is quite similar - check a diesel exhaust pipe. I can't see anything else that can contribute to the formation of the gunk in the EGR and manifold other than extra engine oil. It must be quite a slow buildup over the mileage as the amount of oil is not large, nearly all of it being mist. I didn't look at the EGR in early life - maybe you have a better opportunity to have a peek at some lower mileage ones and form an educated opinion. I think the stuff just builds slowly and continuously, eventually blocking the EGR, manifold and siezing the swirl flaps. There have been plenty of cases of jammed EGR's and swirl flaps from massive buildup.
I also worry about the possibility of chunks of that hard baked on stuff breaking off and damaging the inside of the motor, particularly the valves.
I am prepared to believe that I have exaggerated my problem by chipping the engine - it has always blown a bit more black since chipping and that must add to the recirculated particulates. On the other hand, a lot of my mileage has been done towing and on long trips where the EGR would not work much at all, due to constant boost. I imagine that around town operation with lots of idling and stop/start motoring would be a lot worse.
Overall, EGR's stink, don't they? No problems at all with older Japanese turbo diesels so far. They have only recently adopted the EGR's to try to break into the Euro market. Guess they will develop similar problems in time.

 

[Number_Cruncher]

Messrs Lewis and Dwyer-Joyce are among the experts in diesel engine inlet valve seat recession in the UK.

http://eprints.whiterose.ac.uk/9084/2/Slatter2.pdf

See figure 11.

Although the lubrication isn't well defined, its beneficial effect is clear.

While PCV lubrication isn't well defined, there's a vast yawning chasm between a little lubrication and none.

 

[oigle]

Messrs Lewis and Dwyer-Joyce are among the experts in diesel engine inlet valve seat recession in the UK.

http://eprints.whiterose.ac.uk/9084/2/Slatter2.pdf

See figure 11.

Although the lubrication isn't well defined, its beneficial effect is clear.

While PCV lubrication isn't well defined, there's a vast yawning chasm between a little lubrication and none.

That was a graphic difference in wear for sure. Wonder what level of lubrication they utilised. Seems revs have a great bearing on the wear rate too. Thanks for your input there.
As stated earlier, it is quite open to conjecture as to the amount of oil mist that makes it all the way to the valve seats before settling on all the surfaces along the way. Very minimal at best. I am not arguing that lubric is not good - of course it is. Whether the amount that makes it to the valves from the RCV would make the slightest difference, I don't know but certainly doubt. If I were to start again, I think that dieselmans electronic option would probably be the best along with a blocked off EGR. If that was unable to be used, I would still consider the PCV re-routing in preference to the larger job I undertook, even tho' it looks to be quite successful at this stage. The lack of a water heater certainly has slowed up the warmup and actual final operating temps are lower too for some reason - not quite making 80C now versus about 85C before. Perhaps my thermostat may need replacing. Funny coincidence tho'.

 

[Alex Crow]

Although the lubrication isn't well defined, its beneficial effect is clear.

indeed, having read the paper, i see there is very little drawn in the way of conclusions from the lubricated tests in relation to automotive applications.

it cannot be surprising that lubrication made such a dramatic difference to wear rates, but to conclude what effect pcv will have is not possible from the research undertaken. yes, the effect of lubrication was dramatic, but there was no measure of lubrication levels and no attempt to simulate pcv gasses - oil was used.

 

[Number_Cruncher]

Yes, the paper doesn't fully answer the questions of this thread - but, it was the best freely available one I could find by authors I could have any trust in.

The logic goes like this;

Q) Will removing PCV change the lubrication condition of the valve seats?

A) Yes, there will be a change. It's not possible to quantify it.

Q) Is inlet valve seat recession sensitive to lubrication?

A) Yes, the paper shows this.

Q) Can we be certain that PCV lubrication - even though we can't quantify it - is not vital?

A) No

Q) Is it absolutely safe to delete PCV

A) No - especially not on a vehicle that is used under such arduous conditions.

For more, see;

http://www.tribology.group.shef.ac.uk/research/Automotive/research_projects_valverecession.html

Of course, as an experiment, why not delete PCV?, but, it's an experiment with potentially expensive consequences.

 

[Alex Crow]

Yes, the paper doesn't fully answer the questions of this thread - but, it was the best freely available one I could find by authors I could have any trust in.

The logic goes like this;

Q) Will removing PCV change the lubrication condition of the valve seats?

A) Yes, there will be a change. It's not possible to quantify it.

Q) Is inlet valve seat recession sensitive to lubrication?

A) Yes, the paper shows this.

Q) Can we be certain that PCV lubrication - even though we can't quantify it - is not vital?

A) No

Q) Is it absolutely safe to delete PCV

A) No - especially not on a vehicle that is used under such arduous conditions.

For more, see;

http://www.tribology.group.shef.ac.uk/research/Automotive/research_projects_valverecession.html

Of course, as an experiment, why not delete PCV?, but, it's an experiment with potentially expensive consequences.

impeccable logic, as i would expect from the cruncher of numbers. this quote from your second link from the university of sheffield states it in no uncertain terms...."The drive for reduced emissions from diesel exhausts has led to a reduction in the amount of oil present in the air stream in automotive diesel engines. This, in turn, has led to an increase in the wear of inlet valves and seat inserts in diesel engines.".......it would be nice to see the evidence for this.

this leaves us with the impression that the lower the oil consumption of the vehicle, the worse the valve seat wear! which would we prefer? and does the car using only 250ml / 10,000 miles get any benefit at all from pcv?

 

[Number_Cruncher]

>>This, in turn, has led to an increase in the wear of inlet valves and seat inserts in diesel engines.".......it would be nice to see the evidence for this.

I'm sure they have got the evidence - they have written a book on the subject! I did briefly consult with the Sheffield Tribology group on a rail vehicle project I was working on 10 years ago or so - I was very impressed by their work and their knowledge.

>>this leaves us with the impression that the lower the oil consumption of the vehicle, the worse the valve seat wear! which would we prefer? and does the car using only 250ml / 10,000 miles get any benefit at all from pcv?

We need to tread carefully AP.

Yes, the sump level may drop by as little as 250ml / 10,000 miles, but, does that mean only 250 ml of oil has been consumed? Or does it simply mean that oil consumption and blow-by are well balanced?

The other thing to be aware of is the very unusual conditions at valve seats, unlike most other wearing surfaces in engines, the rubbing velocities are low which may mean that vast quantities of lubricant are not necessary to reduce wear.

I suspect that OM606 engines crossed a boundary line in this respect, and upon the introduction of the turbocharged engine, MB were forced to fit harder seats. I have no evidence for this though, and would be interested to see if the material specs are available.

 

[Alex Crow]

true enough, dilution could be perhaps as much as 1L in this example - who knows. let us also remember that oil consumed is not necessarily vented through the breather - it could be passing the rings, valve guides or turbo seals too. let us also remember that the quantity of oil in the pcv circuit is not all going to coat the valve seats! obviously a very significant quantity will bypass and go straight through into the cylinder.

note that in the lewis and dwyer-joyce modelling the research focus was clearly on materials and operating conditions, with valve seating velocity being a critical factor (assuming given materials). this suggests that optimising valve lobe or tappet wear, lobe design and operating speed would be absolutely critical to an optimised design along with materials selection. the 606 engine was mercedes' first foray into the world of 4v heads on production diesels, it is my suspicion that they took advantage of the lighter valves with higher seating velocities allowing greater time area for given duration, without enough consideration given to increased valve seat wear - perhaps as you suggest the materials were not up to this job.

 

[dieselman]

true enough, dilution could be perhaps as much as 1L in this example - who knows. let us also remember that oil consumed is not necessarily vented through the breather - it could be passing the rings, valve guides or turbo seals too. let us also remember that the quantity of oil in the pcv circuit is not all going to coat the valve seats! obviously a very significant quantity will bypass and go straight through into the cylinder.

note that in the lewis and dwyer-joyce modelling the research focus was clearly on materials and operating conditions, with valve seating velocity being a critical factor (assuming given materials). this suggests that optimising valve lobe or tappet wear, lobe design and operating speed would be absolutely critical to an optimised design along with materials selection. the 606 engine was mercedes' first foray into the world of 4v heads on production diesels, it is my suspicion that they took advantage of the lighter valves with higher seating velocities allowing greater time area for given duration, without enough consideration given to increased valve seat wear - perhaps as you suggest the materials were not up to this job.

I wonder if the turbo 606 has either harder seats as already mentioned by NC or due to being able to produce greater torque at low revs it simply spends more time running at lower revs so the valve speed is reduced anyway.

I suspect there is enough oil in the breather fumes as only the slightest smear of oil is required on a continuous basis, also for the very low consumption engines are we/you sure that the sump level isn't be replenished by diesel passing the rings?

 

[Alex Crow]

.... also for the very low consumption engines are we/you sure that the sump level isn't be replenished by diesel passing the rings?

this is a good point made by NC. how much dilution can the oil survive though? are we running on diesel and particulates at 12,000 miles? if so, what about at 30,000 miles? hard to imagine more than 1L dilution, but we are ALL guessing here.

and as for the turbo 606 not wearing the seats, i actually think it does. i did a head gasket job on one for another garage a few weeks back. it was previously overly lumpy at idle, and when i changed the glow plugs (way back) i noticed severe blow back through the inlet at idle. during the head skim the valves and seats were re-cut, and low and behold it idles sweet now! i seem to remember that this was the suspected problem with turbopete's as well, although i believe he sold it before a remedy was found.

 

[Number_Cruncher]

I found the rearmost 2 seats on my NA OM606 had sunk quite badly, and the 2 in front of them had dark spots - I found this by seeing the exhaust gas blow back out of the inlet ports. The clues were there, in that the deposits on the inlet ports of No. 6 were dryer and dustier than those of the other cylinders.

As per AP, the car ran much better when I refitted the repaired head - although before I made the repair, with the long inlet manifold fitted, the blowback couldn't be heard. I think this is quite a latent failure which only tends to get picked up when the failure becomes so bad it stops the engine starting, or when someone who's awake begins to work on the engine.