Black smoke...blue smoke?

[Steve L22188]

Know there's been some comment on this in the past but can't remember the verdict on smoke color when starting a diesel engine.

Fired up my Yanmar 2GM today and had some black smoke for about 3 seconds. It's only the third time this year the diesel's been run. No exhaust smoke to speak of after that first bit of coughing and cranking and running...again, smoke for only about 3 seconds.

Is black smoke OK? Or bad?

Thanks in advance.

 

[Roadking Larry]

Not a diesel expert but I do have a diesel tractor, a few seconds of black smoke from a cold diesel engine on start-up is no big deal and more or less normal.

 

[CHARLIE STAGE]

My Yanmar 3GM has given me 26years of faithful service and always cold starts with black smoke. Rest assured yours is OK too.

 

[Benny17441]

Black is unburned fuel and blue is burnt motor oil. It is not unusual at startup as a cold diesel engine is not very efficient. What may be unusual is that it seems to have started today or perhaps you had not noticed. These engines need to be used frequently and the fuel needs to be maintained fresh. Make sure you use a fuel additive to limit bacteria growth and help keep the injectors clean. Give the engine a good workout for at least an hour at 90% of Maximum rated RPM and perhaps next time you start it the black smoke will be gone.