"Tar" external deposits Merecedes cyl head?

[BCjohnny]

Must admit not quite seen anything like it before.

Mercedes Vito, fwd 4cyl common rail diesel.

In the recess above the cam cover (and below the plastic "shield") where the solenoid injectors and breather/seperator sit, the whole lot full of tar. Not carbon or that spongey black goo you find in rocker covers, but tar that has set brittle. Seems to be "emerging" from the vicinity of number one injector/breather and oozing along the head and now over the lip onto the side of the head.

Took three hours to chip it all out to expose the injectors. Tomorrow we will delve further, the engine is down on a cylinder (either injector down/low compression). Not my usual fayre, but a mates van no-one else seems in a hurry to touch.

Had many opinions so far, but anyone got any real answers? Apparently it is not uncommon.

Is it somehow connected to the injection pressures involved? Could an injector base washer be leaking and the pressure/combustion causing this? Is it the breather?

Cheers, John.

"It's not always a case of learning more, but often of forgetting less"

 

[MikeHalloran]

All I can think of is some sound deadening that got overheated and ran to where it's not supposed to be, and cooked there.



Mike Halloran
Pembroke Pines, FL, USA

 

[franzh]

Toyota had that same problem with the older MR.2 (we called them the Mister-Two).

The spark plugs went into the top of the cylinder head, between the two cam banks. The valley was covered by a removable plate. In between the plugs was several removable core casting screw in seals. What was happening was there was a slight amount of coolant seeping through these core seals and settling in the valley. The light aromatics would evaporate leaving the heavier glycol compounds which would bake into a heavy tar like substance very closely resembling what you describe. It resisted all conventional attempts at removing, often requiring removal of the head and hot vatting. I have seen the plug valley filled up to the top of the plug ceramic insulators and plug wire boots with this junk and it was nasty.

Franz

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[romke]

the problem is not uncommon with this engine. the substance you see is essentially soot, that should have been separated or taken up by the engine oil and dispersed.

it seems that it is more common with engines that idle a lot or are used for relatively short distances.

if you use and engine oil that exceeds the MB specifications and relatively short oil changes the problem can be avoided. oil quality is vital in this case, although a design flaw problably is the real cause.

 

[dicer]

Sounds like partial coking of oil. It probably gets a bit hot there.

 

[BCjohnny]

Thanks for all the replies, some interesting takes on possible causes.

I think Romke is probably closest. I guess what may have triggered the conversion of soot to tar is the fact that three of the injector base seals were "blowing" into the same area, for some time.

And finally one last question. I'm quite aware of development/manufacturing/distribution/taxes. But £300 for each injector?

John.

"It's not always a case of learning more, but often of forgetting less"