I read your post earlier this morning, so I started investigating. At zero load, the YM240 uses 0.369 gallons per hour to run 2581 RPM. (According to Nebraska Tractor Test 1199.) According to my operator manual, with 9.5-24 tires, maximum speed is 9.11 MPH at 2600 RPM. That works out to 24.7 MPG. However, that is without any load on the engine.

At 4.5 horsepower, consumption is 0.534 GPH, and works out to 17 MPG. If it takes 8.9 horsepower to drive the machine, MPG drops to only 12.5 with 0.726 GPH.

With larger 11.2-24 tires, figures would be 26.2, 18.1, and 13.3 MPG.

I don't think this accurately represents what would happen if the power plant were put into a car, though. It is accurate for driving your tractor down the road, and that is all. Brake specific fuel consumption (BSFC) averages 0.546 pounds of fuel consumed per hour to produce one horsepower. The specific fuel consumption figures are very close to the efficiency of a GM 4.3 liter V-6 (

BSFC of 0.502). I was surprised to learn that the gas V-6 is actually more efficient than the diesel. This will bear more investigation, and has piqued my curiosity. I'm guessing that the gas engine is benefitting from running at peak efficiency (since it is at full throttle) and those figures cannot represent real world partial RPM consumption figures. Running at full throttle makes gasoline engines much more efficient, but isn't representative of real-world usage as a general rule.