For the newer Cummins Diesel
(Tier two and higher), Cummins recommends running it at 100 percent for one-half hour 10 percent of the time. This burns the carbon out of the combustion chamber. Otherwise I run my Cummins B-series turbo diesels at 2400. Diesels do not last as long when run at slower speeds for most of their lives. But on the other hand, the faster you run your Diesel
the worse your miles per gallon. So you have to figure out for yourself which is the best compromise between these two factors. Even with Diesel at $4 to $5 per gallon at most fuel docks in the US, I think it is more cost effective to run your Diesel faster than to run it slower and shorten its lifespan. I'm burning around 20 GPH total (18 knots) on both engines at 2400 RPM
If your healthy engine
cannot reach it's maximum governed speed then you are over pitched or over diameter or both, which means you are lugging your engine
which will shorten its lifespan. Contrary to some peoples opinions doing this is not more fuel efficient. A Diesels specific fuel consumption
does not improve by lugging the engine.
You can get your engines Specific Fuel Consumption curves at Cummins website. The specific fuel consumption is the rate at which fuel is consumed divided by the horsepower produced. The units are grams per second of fuel consumed divided by watts (power) produced.
You can purchase
aftermarket fuel flow meters. When interfaced with your GPS
it can give you gallons per mile. I think the meters might give you a better grasp on what is going on with your consumption versus speed and eventually pay for themselves. My engines are 5 years old and came standard with fuel flow meters. This information has been very helpful to know saving thousands of gallons of fuel.
FloScan Instrument Co. Inc.