There are at least three methods to run a diesel motor on biofuel using veggie oils, animal fats or both. All 3 are used with both fresh and pre-owned oils.

1. Use the oil just as it is-- normally 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 techniques sound most convenient, however, as so often in life, it's not quite that basic.

1. Mixing it

Grease is a lot more viscous (thicker) than either petro-diesel or biodiesel. The purpose of blending 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 blending veg-oil with petroleum diesel or kerosene (very same as # 1 diesel) you're still utilizing fossilfuel-- cleaner than many, but still not clean enough, many would say. Still, for every gallon of

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

People utilize various mixes, varying from 10% vegetable oil and 90% petro-diesel to 90% grease and 10% petro-diesel. Some people just use it that way, begin up and go, without pre-heating it (which makes veg-oil much thinner), and even use pure veggie oil 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 difficult and tolerant motor-- it will not like it but you probably will not eliminate it. Otherwise, it's not wise.

To do it properly you'll need what amounts to an SVO system with fuel pre-heating anyhow, 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 numerous solvents and/or with unleaded gasoline are "speculative at best", little or absolutely nothing is learnt about their effects on the combustion attributes of the fuel or their long-term effects on the engine.

Higher viscosity is not the only problem with using grease as fuel. Veg-oil has different chemical residential or commercial properties and combustion attributes from the petroleum diesel fuel for which diesel engines and their fuel systems are developed.

Diesel engines are state-of-the-art devices with very accurate fuel requirements, especially the more modern-day, cleaner-burning diesels (see The TDI-SVO debate).

They're hard but they'll just take a lot abuse. There's no assurance of it, however utilizing a mix of approximately 20% veg-oil of good quality is said to be safe enough for older diesels, particularly in summer.

Otherwise using veg-oil fuel requires either an expert SVO solution or biodiesel. Mixes and blends are normally a bad compromise. But blends do have a benefit in cold weather condition.

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