I have been tracking fuel usage in my automobiles and power equipment for over ten years and thought I would post the figures for the mowers and tractor here in case anyone is curious. Maybe others do the same and wish to share.
1. Self-propelled mower, mechanical drive, thirty-six inch deck, side discharge, old style L head Briggs & Stratton 12 hp engine. 1.88 hours per gallon
2. Self-propelled mower, hydrostatic drive, thirty-six inch deck, grass catcher with blower, single cylinder Kawasaki OHV 13 hp engine. 1.53 hours per gallon
3. John Deere 4 wheel drive compact tractor, standard transmission, three cylinder Yanmar diesel engine, 26 hp gross. 2.10 hours per gallon
These figures are mostly to satisfy my curiosity. There is really nothing I can do to improve them much except maybe mow more often. I always buy premium gas for the gas engines and add Sta-Bil and Mystery Oil to the gas. Diesel fuel is treated with Howes Diesel Treat.
The diesel tractor seems to be far more efficient than the gas mowers but the tractor gets a lot of hours doing things that do not demand a lot of power output from the engine. If memory serves me the engine is rated at about one gallon per hour at something like 90% output. The gas mowers are getting more hours under a greater load percentage than the tractor.