Black smoke vs white smoke (Both unburnt fuel)

White smoke = unburnt
Black smoke = partially burnt but not completely utilized.

Thats how it was explained to me.

Partial combustion may be the result of not enough air, like a clogged Airsep or a worn out turbo.
Could be the engine is overloaded like the wrong prop pitch or a filthy bottom,shaft, wheels....

White smoke is actually vaporized diesel fuel, it is not really white, it is clear but the refraction of light makes it look white. This is why water in the atmosphere makes white clouds.

When the engine is cold and/or compression is low, as during a start, the governor supplies a large quantity of fuel as it attempts to bring the engine up to idle speed or whatever is selected. Because the inlet air is cold (relatively) and much of the fuel is not vaporized completely and does not reach a high enough temperature to ignite, it leaves as microscopic drops that appear white.

When a hot engine receives more fuel than it can burn as in an overload condition or if there is some obstruction to charge air delivery, the fuel is heated enough to form carbon particles - soot. But since the combustion chamber lacks enough oxygen to combust completely, the unburned carbon particles leave as a dark cloud.

Hi All

I have two Cats 3208 V8 turbos. Recently we have done a major overall, striped the motor to bear minimum and rebuilt them. We did a seatril just the other day, the motors ran at ideal well, but the minute we put them under load and the revs exceeded 1900 the port side motor had a pitch black cloud of smoke being emitted, where as the STB motor had no smoke, to confuse the matter, both motors are only running at a max of 2100 revs under load were as before they ran at 2800 at load. I approached the mechanic and explained the problem and refused to pay him for the work until the motors are right. He then explained to me that the setting on the stb motor injector pump is not right, and could be set up for a grader instead of a high revving boat. Could this be the problem or is there something else that’s wrong?

It sounds like you have a mechanic -al problem.

Best explanation for this I have ever seen, thanks!

Agree on that, it is in my notes!
Thanks Marmot.
G