yes, waste frying oils are a good fuel for old-school engines

Many ppl still don't trust veggie fuels at all, not even the ethanol as a possible replacement for petrol, and get even more unfavorable to the usage of veggie oils for old diesel engines. It does work properly, better in a mechanical indirect injection, because lower pressure and slower combustion process starting at the prechambers allow to a more complete combustion of glycerin, so there are fewer residues to stick to the cylinder walls or the piston rings. Few adaptations can be adviced, mostly to pre-heat the oil in order to decrease its viscosity for an improved flow but may not be required at all. Unlike direct injection engines that may not just experience the acumulation of glycerin residues and lubricator oil contamination, indirect injection actually can achieve fuel savings in a magnitude greater than 20%. In a Toyota Hilux from mid 80s with the L-type engine, pretty much underpowered to be fair, it could return some 5.9L/100KM (17KM/L) and was a bit better throttle-responsive too.