JimC,
Very interesting web site. I bookmarked it.
We engineers used to have some figures for automobile fuel consumption. These were:
30 Ton-mpg -- gas e.g. a 2,000 # car will get 30 mpg
45 Ton-mpg -- Diesel e.g. a 2,000 # car will get 45 mpg
The gas figure is 25-50% higher now, what with better fuel control via fuel injection, etc. for emissions. My VW, for instance, is 2,700 # and gets 32 mpg. My Tacoma is 2,900 # and gets 26 mpg. Back then diesel was 50% better than gas. The article for tractors didn't show this big a difference. Think they're closer for cars now, too, with almost all cars on fuel injection.
What guys can do to keep track is to put down their engine hours along with fuel container amount put in each time they fuel up.
Ralph