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

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

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 first 2 techniques sound most convenient, however, as so typically in life, it's not quite that basic.

1. Mixing it

Grease is a lot more thick (thicker) than either petro-diesel or biodiesel. The function of mixing 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 most, but still unclean enough, numerous would say. Still, for every single gallon of

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

People utilize various blends, varying from 10% grease and 90% petro-diesel to 90% vegetable oil and 10% petro-diesel. Some people just use it that way, launch and go, without pre-heating it (which makes veg-oil much thinner), or even use pure vegetable 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 won't like it but you probably will not kill it. Otherwise, it's not smart.

To do it effectively you'll require 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 blends.

Blends with different solvents and/or with unleaded gasoline are "experimental at best", little or nothing is understood about their impacts on the combustion characteristics 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 homes and combustion attributes from the petroleum diesel fuel for which diesel engines and their fuel systems are designed.

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

They are difficult however they'll just take a lot abuse. There's no guarantee of it, however utilizing a blend of approximately 20% veg-oil of good quality is stated to be safe enough for older diesels, especially in summertime.

Otherwise utilizing veg-oil fuel requires either an expert SVO option or biodiesel. Mixes and blends are generally a poor compromise. But blends do have an advantage in cold weather.

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