Black Exhaust Stains On Transom

[maxcontax]

I took a diesel maintenance course a few years back. the instructor was not impressed with how sailors treat diesel engines--he wanted us to run them nearly wide open and under load and long enough for them to get hot. We run them at low rpm, which means the Advance of about 17 degrees is wrong and the burn is inefficient. We run them cold, just enough to get out of the harbour. I think carbon buildup is the cause of the black and the solution may be 6 hours of running the engine at near maximum rpm. the problem with that, as we explained to the instructor, was loading up the prop and drivetrain because you are then trying to push the boat faster than hullspeed, which is not good for the rest of the system. Mine gets an "Italian Tuneup" twice a year, it is a 1984 raw water cooled Volvo and it runs fine.

[eyebbober]

Thank you everyone! Im thinking its normal. Water is shooting out the back and its not overheating.

I need to know though what an Italian Tuneup is.

Thanks!

[maxcontax]

Italian tuneup: warm up the engine and then run it close to wide open for 10 minutes. It blows out the carbon. Optimum rpm for the fixed advance on a diesel is nearly wide open for most. Auto/truck diesels have variable advances so they are fuel efficient at any speed, but marine diesels are fixed advance. They seem to set the advance for when you would be most in need of power, ie using full throttle. at 2150 rpm, where mine lives most of its life, it is not optimum. Nothing to be done about it, just the way they set them up. This is why they carbon up--this and too much time running cold.

[ct]

White smoke is caused by engine oil burning. Check valve guides and seals . However you aren''t complaining of white smoke.

The most common cause of black smoke from a diesel engine is injector timing being too far advanced or dirty injectors.

When you first give some throttle, you might and should get a slight puff of black smoke which clears.

[hamiam]

hunh? i thought blue smoke was evidence of engine oil burning?

[ct]

Engine oil smoke has been described as "blue", however most people complain of a "white-ish" or "white" smoke.

I agree that this can be confused with steam coming from the exhaust which might indicat a head-gasket problem.