Hi Guys

After a bit of advice.

OM366A engine in a Mercedes 1617.

Last few days she has been belching out exhaust, way more than usual, even when at running temperature, and have been gaining a significant amount of engine oil.

Initially thought it was water getting in the oil as the smoke was a whiteish colour.

However, she is holding her temperature very well, she has not needed any water adding to the header tank, and when we changed the oil there was no sign of water in the sump/oil drained out.

Therefore thoughts lead us to think she is leaking diesel into the oil supply. The oil does appear quite thin, and the oil filter element had a purple tinge to it suggesting diesel contamination.

First thought: injecters not tight, so leaking diesel into oil supply in the cylinder head.

However, all injecters tight, no concerns there. Return line also tight (where it screw into the side of each injecter)

She has full power, drives along fine as usual, but belching out smoke and like we say, gaining oil.

Looking through the Merc manual, I discovered a page detailing the replacement of O rings below where the injectors sit.

So, if you pull out the injectors, you are left with the cavity they sit in. But there is a protective sleeve in this cavity, that can be removed with a special merc tool, and apparently an O ring sits below this protective sleeve.

These O rings do come with the head gasket set, always have done, but I've never acutally replaced them. The manual suggests that if these O rings are old/perished, then water can get into the water supply. But we are convinced it is not water, but diesel.

Do you guys think diesel could get into the oil supply from these O rings? I guess if the injectors are spraying into the combustion chamber, there is potential that it can escape into the oil supply due to these O rings being worn?

Also thought the timing of the engine is wrong so delivering too much fuel, leading to excess diesel in the combustion chambers hence the excess smoke, but we have not played around with the timing on the injector pump, so find it hard to believe this is the issue.

Any thoughts appreciated.

David

think it more likely to be the lift pump that sends oil to teh injector pump. Had the same thing on my Massey Ferguson. Usually it is the rubber diaphragm that splits.

Thanks for the thoughts.

Only thing that makes me think it might not be that....if the rubber has split causing diesel to leak into the engine block (and therefore the oil supply), then surely air in turn can get into the diesel supply via the lift pump? That would result in loss of power/difficulty starting etc as would need to bleed the fuel system of air.

This is not the case, she starts perfectly every time and no loss of power at all.

However will check regardless.

Any other thoughts appreciated.

Likely an injector has failed and is leaking fuel into a cylinder and then trickling down into the sump passed the piston rings when the engine is stopped. The white smoke is an indication of over fuelling/unburnt fuel when the engine is running.

Best thing would be to get each injector tested and calibrated.

Thanks for the thoughts Roger.

I forgot to mention we had all 6 injectors out less than a month ago. Pressure tested them, all fine, no signs of leaking, atomizing the diesel perfectly.

The nozzles are only 30,000kms old also.

So can't believe they are leaking this significantly having only tested them a month ago.

On a 1,000km drive through Europe this week she gained approx 2-3 litres of oil (and we think it is diesel in the oil).

you need to watch for level getting high enough that it starts to run on the sump oil (runaway) , also there is a serious risk of damage to bearings with diesel diluted engine oil .

I had the same problem with Mercedes 352A in my unimog. Changed the fuel lift pump and cured the problem. A repair kit is availiable for the lift pump.

Hi tac2Rman

Yes, agreed. We changed the oil when we noticed it had gained 2 litres or so after a days drive.

Then we checked all the injectors area, tightened everything, hoped we had cured it, and then it continued, so swapped the oil again.

We are not driving it until we solve this problem, so hopefuly no damage done so far.

Neil, agreed, we will check the lift pump. If we unbolt it from the engine block and manually prime it with the priming handle we should notice diesel leaking around the back (ie the side which bolts onto the engine block)

Any other thoughts appreciated.

Just a thought.....if lift pump is leaking diesel into the engine block where it bolts on, then surely it can draw in air as well? That would lead to starting problems and power issues as air in the diesel system.......as before, we have had no power issues and she starts fine first time.

When the fuel lift pump on my Unimog was leaking diesel into the engine oil I had no running problems or starting problems. Another possibillity is a crack in the injector leakoff pipe .

Thanks again for suggestions Neil. Yes, we will take return pipe off and blow compressed air down it and see if any holes/fractures this would piss diesel into the oil supply if the culprit.

Will report back. Thanks for all your thoughts.

All you need to do is take the pump off and work the operating lever. Diesel will squirt out from the split in the diaphragm. It will pump enough to feed the injector pump without any injection problems. The diluted lube however will lower oil pressure, and wreck your crank and big end bearings. the diesel will dissolve the carbon in the piston ring grooves and allow it to piss oil into the cylinders.

You have spent more time debating this than fixing the fault would have taken.

Hi Oldbmw

Thanks for your advice. Can't check the problem myself as I am not currently with the truck.

I had the same fault with my Massey tractor. It has a fuel tank above the engine and I first found it very weird that my oil level was rising, and oil pressure dropping. Took me a while to figure out how it was happening. At first I thought the fuel was gravity fed direct to the injector pump, but it isn't. The Tractor uses a lift pump to lower the diesel .

The four gallons or so of lube oil/diesel worked well in my oil burning stove

In the end: a leaky injector!!

Couldn't believe it. We had all 6 injectors out just 4 weeks before this problem happened. We had hooked them all up to a pressure tester. They all held 180-200 under load, absolutely zero sign of dribbling or leaking, and the spray pattern very good (for all of them).

Yet 4 weeks later one started leaking.

Injector in cylinder 1 was the culprit. It must have been leaking significantly to have caused the amount of smoke and oil gain we were experiencing.

Anyway, problem solved, the old girl is back to normal thankfuly.

Cheers for all of your advise much appreciated.

David