Personally I would go for a good quality gas engine on the splitter. How many hours do you run the splitter in a season, are you commercial? I am still splitting with a 15 year old MTD 20 ton splitter using the original Briggs gas engine. I heat with wood and regularly split a tri-axle load of logs each year. Although I try and do my splitting in the Fall, on occasion I find myself working in very cold weather, wonder how the diesel would start, especially with a pull starter. Also, 5 gallons of gas will split a lot of wood with my little 20 ton unit, I can't magine the fuel savings would offset the expense of a diesel engine. Good luck, keep us posted.