Received this in an email and thought that I would share it
Hints from Admiralty Yacht Sales -- Diagnose your diesel engine
While this is not intended to be an exhaustive list of methods to diagnose your diesel engine's general health, there are several non-technical techniques to check the health of your engine. Make sure your engine is warmed up before diagnosis.
Diagnose your diesel engine's running condition by the color of its exhaust:
Black smoke - Indicates unburned fuel/highly loaded condition
Black smoke with oil sheen and soot on the water
- In situations where the boat has reached hull speed and the engine has enough power to try to make it go faster, black smoke will result. Back off the throttle a few hundred RPM's until the black smoke disappears or reduces to gray smoke.
- May indicate plugged, worn or dirty injectors. Running the engine hard for 15 minutes or so may clean up the exhaust. If after this "blowing out" period the black smoke continues, injector service may be necessary.
- Indicates normal running condition. All diesels produce some level of gray smoke and may leave a sooty film on the transom of the boat. If a great deal of soot is present, see "black smoke".
- Probably indicates steam. Check engine temperature and volume of exhaust water to insure the engine is running at the proper temperature. In cold weather, white smoke is normal when engine is at operating temp.