"Rod McInnis" wrote in message ...
"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?

They are both smoking at all speeds, port more than starbord. Other than the
smoke (again, not exceesive but more that I would like)



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.

This is taken full throttle (I don't know what else to call it either)
under load (about 16knts).

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.

there seems to be more smoke at idle speeds. That may be because the
there is air movement.

I talked to the turbo rebuild tech today, he found one bad turbo, (exhaust
blade hitting the housing) the port side. He said the starboard was in
fair condition.

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.

Yeah, I don't blame you for being confused, I worked out this elaborate
scenerio to explain the lack of blowby.



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.

Whoa! 125/injector...
I agree, I will be removing them as soon as I get the turbos back on. (hopefully
this weekend).


Thanks a lot for the response Rod.