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

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

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 first two methods sound simplest, however, as so typically in life, it's not quite that basic.

1. Mixing it

Vegetable oil is a lot more viscous (thicker) than either petro-diesel or biodiesel. The function of blending it or blending it with other fuels is to reduce 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 (like # 1 diesel) you're still utilizing fossilfuel-- cleaner than a lot of, however still not clean enough, many would say. Still, for every gallon of

grease you utilize, that's one gallon of fossil-fuel conserved, which much less climate-changing carbon in the environment.

People use various blends, varying from 10% grease and 90% petro-diesel to 90% veggie oil and 10% petro-diesel. Some people simply use it that method, launch and go, without pre-heating it (that makes veg-oil much thinner), or perhaps use pure veggie oil 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 an extremely difficult and tolerant motor-- it will not like it but you most likely will not eliminate it. Otherwise, it's not sensible.

To do it properly you'll require what totals up to an SVO system with fuel pre-heating anyway, preferably utilizing 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 "speculative at finest", little or nothing is understood about their impacts on the combustion attributes of the fuel or their long-term effects 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 attributes from the petroleum diesel fuel for which diesel engines and their fuel systems are developed.

Diesel motor are high-tech devices with extremely exact fuel requirements, especially the more modern, cleaner-burning diesels (see The TDI-SVO controversy).

They are difficult but they'll only take a lot abuse. There's no assurance of it, however using a mix of up to 20% veg-oil of great quality is said to be safe enough for older diesels, specifically in summer season.

Otherwise using veg-oil fuel needs either a professional SVO service or biodiesel. Mixes and blends are generally a poor compromise. But mixes do have an advantage in cold weather condition.

Just like biodiesel, some kerosene or winterised petro-diesel fuel blended with straight vegetable oil reduces the temperature at which it starts to gel. (See Using biodiesel in winter) More about fuel blending and blends.