There are at least three ways to run a diesel engine on biofuel utilizing vegetable oils, animal fats or both. All three are utilized with both fresh and pre-owned 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 blend it with a solvent, or with gas;

3. Convert it to biodiesel.

The very first 2 approaches sound most convenient, however, as so typically in life, it's not quite that easy.

1. Mixing it

Grease is much more viscous (thicker) than either petro-diesel or biodiesel. The function of mixing it or mixing it with other fuels is to reduce the viscosity to make it thinner so that it flows more freely 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 using fossilfuel-- cleaner than many, however still not tidy enough, many would state. Still, for every gallon of

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

People utilize different blends, varying from 10% vegetable oil and 90% petro-diesel to 90% veggie oil and 10% petro-diesel. Some people just utilize it that method, start up and go, without pre-heating it (which makes veg-oil much thinner), or even utilize 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 a really hard and tolerant motor-- it won't like it but you most likely will not kill it. Otherwise, it's not wise.

To do it effectively you'll require what amounts to an SVO system with fuel pre-heating anyhow, 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 various solvents and/or with unleaded gasoline are "experimental at best", little or absolutely nothing is learnt about their results on the combustion qualities of the fuel or their long-lasting effects on the engine.

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

Diesel engines are state-of-the-art machines with really exact fuel requirements, particularly the more modern-day, cleaner-burning diesels (see The TDI-SVO controversy).

They're hard but they'll only take a lot abuse. There's no warranty of it, but using a mix of up to 20% veg-oil of excellent quality is stated to be safe enough for older diesels, specifically in summer season.

Otherwise using veg-oil fuel requires either an expert SVO service or biodiesel. Mixes and blends are usually a bad compromise. But mixes do have a benefit in winter.

As with biodiesel, some kerosene or winterised petro-diesel fuel blended with straight veggie oil lowers the temperature at which it begins to gel. (See Using biodiesel in winter) More about fuel blending and blends.