you just opened a can of worms , where to start ? well guess who invented the diesel eng. Rodolf diesel , he tried a lot of fuels like coal dust , amonia and ended up with the origanal [ not the alternative ] vegtable oil so farmers could make there own fuel, then the guys making gas figured that they had a market for one of the waste byproducts of making gasline , now we have newsspeak [ for later , gas being the alt, not vegi oil ] vegi oil has a little less btus. but more centain , also a lot more lube , infact some of the best additives are a high % of it , the used stuff works but the best way for the long term is to use a prossess called esterfication , to remove the gliserin and water, if you switch to a high % [ maybe 30% or more ] than you have 2 other issues , the vegi will take a lot of varnish , gums and other dirt [ diesel being a very dirty fuel [ except for jet fuel ] so you'll need frequent fuel filter changes in the begining, next is if you have about a 94 or earlyer high % of vegi will soften rubber hoses and seals to the point of causing other problums , but we seem to enjoy making things better so the effort is worth it , now add to that if you can find a place that does not over charge [ this maybe being the biggest job ] I've heard of some places selling for 1. 70 gal. and I'ved checked out making it for . 40-50 cents gal. To also help try this web site MU boidiesel- biofuels research [I wish my memory worked so I could postit].