There are two kinds of smoke from either Diesel or SI engine. First is
white/bluish smoke. Although we frequently say an engine smoking like
that is 'burning' oil, it is not really burning it. In fact, that is
vapor from hot oil, unburned, and comes from oil leaking into hot
cylinder from bad rings or valve seals, and is the same in SI or CI.

Second kind of smoke is black smoke, or soot. This has somewhat
different but related causes in SI and CI engines. In either case it is
due to rich mixture resulting in incomplete combustion, but the
technical details on exactly how the soot forms are different. In the CI
(Diesel) it usually means misadjustment or problem in fuel (injection)
control.

Engineman1 wrote:

A friend is thinking of buying a yacht with twin diesel engines. He doesn't
trust the people who inspect boats because he believes they are in cahoots with
the yatch brokers. He asked me if I'd take a look at the engines in the boat he
made an offer on. Are there some things I can check on without taking a lot of
time and using expensive equipment? He suggested checking the exhaust for smoke
but since diesels burn oil anyway I wouldn't expect to tell much from that. Oil
analysis is out because the owner just changed it.
engineman1

--
Don Stauffer in Minnesota

webpage- http://www.usfamily.net/web/stauffer