Smoke from Mercruiser VM Diesel .....cause ?

[Momac]

A friend has new to him 1999 built boat which he bought late last year . 700 hours on twin VM diesel (Mercruiser) 6 cylinder engines on outdrives. River use. One shared fuel tank.
Port engine had started to smoke a bit . White, maybe slightly grey, smoke.

Starboard engine is fine with no smoke at all that we can see - it was rebuilt into a new block at the expense of a previous owner .
The boats early years were on French rivers and little use .

Turbo removed and checked by turbo specialist but declared within new tolerances so it was refitted without being refurbished.
No engine oil appears to be consumed . Oil half way between the dipstick marks.
Fuel filter changed
The foam air filter was very oily and perished so he changed it but that did not cure the smoke problem.
Went for a short blast on Sunday when no one was looking (speed restricted area ) and a cloud of muck was ejected from the exhaust , then it cleared . Back at the pontoon there was virtually no smoke .

The following morning on cold start up just wisps of smoke which seems quite normal/acceptable yet still it is noticeably from the port engine.

Might the fault be cured by the Italian tune up and if so what was the most probable cause of the oily air filter and the smoke ?
I wonder if the smoke will return with further use . This remains to be seen.

 

[oldgit]

How many hours on smokey engine verses clean one.
Injectors may have been refurbed/ replaced on engine that was repaired.
One of my engines was rebuilt some time in its life it now has 500 hours on the clocks , its as clean as whistle.

The other untouched engine has 1100 hours and will give a slight hint of smoke if you look hard enough, probably the injectors need sorting but it certainly wont be any time soon.

 

[Momac]

It was more than a hint of smoke (but not embarrassingly smokey) before the fast run
I think the rebuilt engine was done at about 350 hours . A lack of use issue perhaps.

Injectors are possibly the cause - just looking for all possibilities.
Maybe further regular use will ease the issue .

 

[oldgit]

It was more than a hint of smoke (but not embarrassingly smokey) before the fast run
I think the rebuilt engine was done at about 350 hours . A lack of use issue perhaps.

Injectors are possibly the cause - just looking for all possibilities.
Maybe further regular use will ease the issue .

Chum of mine has just bought a Broom 33 with pair of 180 HP Mercruisers, brief bit of smoke on start but soon clears, very quiet and smooth engines.
..................but simply not man enough to move the Tub of Lard known as the Broom 33 beyond a sedate Thames crawl.

 

[Momac]

I think these are 250hp?
Ample power in a Hardy Seawings 355 (the Hull was probably built in the same shed as the Broom).

 

[oldgit]

It appears the Broom 33 is a known sluggard . In a boat test of the period claims of 22 knots suggested by Broom if the boat was fitted with a pair of 200HP Volvos.
It dismally failed to achieve this on the trial and mutterings of later prop revisions to sort this out.
Cynics might suggest on all/most boat tests the boat is loaded as lightly as possible, even down to some standard fit items curiously missing and to be "fitted later."
Various anecdotal stories of owners trying to sort the problem, then either putting up with it or selling on.
Prop sellers helpfully suggesting either 3 or 4 blade swaps at great expence and precious little success.
If anybody is looking for a beautiful Broom 33 that can be outperformed by a one legged seagull, PM me.

 

[Portofino]

Sounds like the difference is in the rebuilding.
As the oil level remains constant it’s not rings ,or valve seats .That leaves injectors fouling up from low river use EGTs .Hence the Italian tune effect of reducing the smoke .
Eventually the rebuilt one s exhaust will match the none rebuilt one as agglomerations development occurs in that due to lower EGT s and lower cylinder pressure + temps . Reducing the tip cleanliness of the rebuilt one .

But the hrs and usage is pretty low to jump to any meaningful conclusions.
Ask him to put 50 hrs on them @ design cruising speed then report back .
If he can’t I suspect so in a speed restrictions river then there’s nothing more to be done basically.

 

[rafiki_]

If no oil being burnt, then it could be overfuelling. Engines are hardly working at river speeds. It might make sense to have the injectors checked, but might just be a problem at river speeds. Engines may not be getting fully up to temp as the load is so low.

 

[Momac]

Sounds like the difference is in the rebuilding.
As the oil level remains constant it’s not rings ,or valve seats .That leaves injectors fouling up from low river use EGTs .Hence the Italian tune effect of reducing the smoke .
Eventually the rebuilt one s exhaust will match the none rebuilt one as agglomerations development occurs in that due to lower EGT s and lower cylinder pressure + temps . Reducing the tip cleanliness of the rebuilt one .

But the hrs and usage is pretty low to jump to any meaningful conclusions.
Ask him to put 50 hrs on them @ design cruising speed then report back .
If he can’t I suspect so in a speed restrictions river then there’s nothing more to be done basically.

Thank you
The owner intends to use fuel additive / injector cleaner in the hope that this will improve things.
I do think a good long run at planing speed would do it no harm and I will suggest this sooner rather than later.

Engines may not be getting fully up to temp as the load is so low.

That is almost certainly so but does not explain why one engine is smoke free and the other is not.

 

[Assassin]

White smoke suggests water and this can come down to many things, I would suggest a compression test as he can do this himself, followed by a leakdown test to check if water is entering the cylinders.

A word of caution for additives, while they are a good idea for suspected injector issues, always use a slow working type as the rapid acting types can dislodge so much contamination, so quickly, that such a sudden release can cause more issues.