i have been burning straight oil, not converting it to bio, just filter it and dump it in the tank. been doing it for 5 years now. the tractor gets up to 50% mix in the tank. the old deere is pretty good on fuel, at 6 gallons per hour if i get 15 gallons a week to toss in the tank it isnt much but it helps.
use an old milk sock from the dairy pipeline for filtering the oil.

the bigger tractor has a "P" series pump and higher nozzle pressure so it can handle thicker oil in the tank.

the little 4020's have the rotary pump and pencil injectors, they run about 1000psi lower pop pressure, it can handle up to a 25% mix.

starting takes a couple more cranks in the morning. little more blue smoke at idle. gained about 100 rpm in the field. little more black smoke than the newer fuels.

on the new trucks i am not sure how the unit injectors are for sensitivity to any contamination or what not. in theory they should be great for running veggie oil or drain oil since they are at a 25k lbs pop pressure.