There are at least three methods to run a diesel engine on biofuel utilizing vegetable oils, animal fats or both. All 3 are used with both fresh and pre-owned oils.
1. Use the oil simply as it is-- generally called SVO fuel (straight vegetable oil);
2. Mix it with kerosene (paraffin) or petroleum diesel fuel, or with biodiesel, or mix it with a solvent, or with fuel;
3. Convert it to biodiesel.
The very first two approaches sound easiest, however, as so frequently in life, it's not rather that simple.
1. Mixing it
Vegetable oil is far more viscous (thicker) than either petro-diesel or biodiesel. The purpose of blending it or mixing it with other fuels is to lower the viscosity to make it thinner so that it streams more easily through the fuel system into the combustion chamber.
If you're mixing veg-oil with petroleum diesel or kerosene (same as # 1 diesel) you're still utilizing fossilfuel-- cleaner than most, however still unclean enough, many would state. Still, for each gallon of
grease you use, that's one gallon of fossil-fuel conserved, which much less climate-changing carbon in the atmosphere.
People use numerous blends, varying from 10% vegetable oil and 90% petro-diesel to 90% grease and 10% petro-diesel. Some people simply utilize it that way, launch and go, without pre-heating it (that makes veg-oil much thinner), or perhaps utilize pure grease without pre-heating it, which would make it much thinner.
You might get away with it with an older Mercedes 5-cylinder IDI diesel, which is a very difficult and tolerant motor-- it won't like it but you most likely won't kill it. Otherwise, it's not sensible.
To do it properly you'll require what amounts to an SVO system with fuel pre-heating anyway, ideally using pure petro-diesel or biodiesel for starts and stops. (See next.) In which case there's no requirement for the blends.
Blends with different solvents and/or with unleaded gasoline are "experimental at best", little or nothing is known about their effects on the combustion qualities of the fuel or their long-term results on the engine.
Higher viscosity is not the only issue with using veggie oil as fuel. Veg-oil has various chemical residential or commercial properties and combustion qualities from the petroleum diesel fuel for which diesel motor and their fuel systems are created.
Diesel motor are high-tech machines with very accurate fuel requirements, specifically the more contemporary, cleaner-burning diesels (see The TDI-SVO controversy).
They are difficult however they'll only take a lot abuse. There's no guarantee of it, however utilizing a blend of approximately 20% veg-oil of great quality is stated to be safe enough for older diesels, particularly in summertime.
Otherwise using veg-oil fuel requires either a professional SVO solution or biodiesel. Mixes and blends are generally a poor compromise. But mixes do have a benefit in cold weather.
As with biodiesel, some kerosene or winterised petro-diesel fuel blended with straight vegetable oil reduces the temperature level at which it begins to gel. (See Using biodiesel in winter) More about fuel blending and blends.