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There are at least three methods to run a diesel engine on biofuel using vegetable oils, animal fats or both. All 3 are utilized with both fresh and used oils.

1. Use the oil just as it is-- typically called SVO fuel (straight grease);

2. Mix it with kerosene (paraffin) or petroleum diesel fuel, or with biodiesel, or blend it with a solvent, or with gasoline;

3. Convert it to biodiesel.

The first two techniques sound most convenient, however, as so often in life, it's not rather that simple.

1. Mixing it

Grease is a lot more thick (thicker) than either petro-diesel or biodiesel. The purpose of mixing it or mixing it with other fuels is to decrease the viscosity to make it thinner so that it streams more freely through the fuel system into the combustion chamber.

If you're blending veg-oil with petroleum diesel or kerosene (exact same as # 1 diesel) you're still utilizing fossilfuel-- cleaner than a lot of, but still not tidy enough, many would state. Still, for each gallon of

vegetable oil you utilize, that's one gallon of fossil-fuel saved, and that much less climate-changing carbon in the atmosphere.

People use various mixes, ranging from 10% vegetable oil and 90% petro-diesel to 90% veggie oil and 10% petro-diesel. Some people simply use it that way, start up and go, without pre-heating it (that makes veg-oil much thinner), or even utilize pure grease without pre-heating it, which would make it much thinner.

You may get away with it with an older Mercedes 5-cylinder IDI diesel, which is an extremely tough and tolerant motor-- it will not like it but you probably won't eliminate it. Otherwise, it's not wise.

To do it properly you'll need 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 need for the mixes.

Blends with different solvents and/or with unleaded gas are "experimental at best", little or absolutely nothing is understood about their impacts on the combustion qualities of the fuel or their long-lasting impacts on the engine.

Higher viscosity is not the only issue with using vegetable oil as fuel. Veg-oil has different chemical homes and combustion qualities from the petroleum diesel fuel for which diesel engines and their fuel systems are developed.

Diesel engines are modern makers with very exact fuel requirements, particularly the more modern, cleaner-burning diesels (see The TDI-SVO debate).

They are difficult but they'll only take a lot abuse. There's no assurance of it, however utilizing a mix of up to 20% veg-oil of excellent quality is stated to be safe enough for older diesels, particularly in summertime.

Otherwise using requires either a professional SVO option or biodiesel. Mixes and blends are normally a poor compromise. But blends do have a benefit in winter.

Just like biodiesel, some kerosene or winterised petro-diesel fuel blended with straight grease decreases the temperature level at which it begins to gel. (See Using biodiesel in winter season) More about fuel mixing and blends.