Fast Idle

[Jaxon]

Hey guys, what is the actual mechanical purpose of fast idling a diesel engine? I've been doing it for many years, and I don't even know the purpose. I'd heard carbon build up, etc, but whats the truth?

[madmatt]

prevents carbon build up and in some cases, excessive oil consumption.

[2jranch]

In the old days with big diesels, we raised the idle speed to burn off the fuel so it wouldn't wash the cylinders. I still believe that is the main reason other than for warming up a cold engine. When it's real cold diesel will not stay at operating temp unless the idle is raised, consequently they will wash cylinders and carbon up. Idling for long period is generally not good for an engine unless it is edled up to 1100 to 1300 rpm.

[Jaxon]

THanks smile.gif