"Mike" wrote in message

I have 2 Cummins 6bt5.7M (4k hours) that are beginning to smoke and
leave a film at the exhaust (sea water output).

Is this at all speeds, or only under wide open throttle? (okay, diesels
aren't throttled, but I never picked up what the proper term for a diesel
is....). If it is WOT only, is this slick so obvious you can see it going
full speed?

Other than the oil in the water, how are the engines running? Still giving
you the same performace as before? How about fuel usage?


3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual
calls for 20-25psi.

Is this measurement taken while under load, or while in neutral? I
wouldn't expect the turbos to be working very hard unless the engines were
heavily loaded. Engine RPM does not indicate turbo RPM.

OK, now for my diagnosis;
The smoke and sheen that I see are unburned diesel.

Probably.

The cause is low turbo pressure not getting enough air into the
cylinders.

Only if this problem is occuring at or near WOT conditions. If this problem
happens at idle speeds (which is when I would expect you would be able to
see the sheen in your wake) then it isn't the turbo.

The low turbo pressure is
Caused by bad oil seals in the turbos allowing crankcase pressure to
be reduced by the vacuum of the turbo compressor.

I don't follow you here.

If there aren't any obstructions in the turbo intake (like an air filter)
then there shouldn't be much vacuum generated. I am not familiar with this
engine at all, so I don't understand how the crankcase pressure and turbo
are related (the turbos I am familiar with have been mounted external to the
engine and don't have any connection to the crankcase that could leak).

If the problem were bad oil seals, however, then I would expect that there
would be a loss of oil. If the leak went external then it should be making
a mess in the engine room. If the leak went internal then I would expect it
to just be burned, only showing up in the fact that you have to add oil
often.



Anyone have any feedback? The engines are honey's. They have never
failed in the 10 years we've owned the boat ( 3000hrs). The smoke is
not a killer yet, but I would like to solve the problem before it gets
worse.


When was the last time you had the injectors serviced?

A diesel engine requires a little bit more than just squirting the fuel into
the cylinder. Part of the injectors job is to atomize the fuel as it is
injected so that it can burn. Vaporized fuel will ignite and burn. Liquid
fuel will NOT burn.

A worn injector can allow a portion of the fuel to enter as a liquid stream.
Some of this will boil and burn, but portions of it will remain liquid, not
burn and then go out the exhaust, causing your problem.

The last time I had injectors serviced it cost me $125 an injector. I took
them off, brought them down to a shop that specializes in diesel fuel
systems. They had them about a day and then I picked them up and put them
back on. An engine I was about ready to throw the towel in on ran great
after that.

If your injectors have 3000 hours on them, then I wouldn't hesitate to have
them serviced.


Rod