There are at least three ways to run a diesel engine on biofuel using veggie oils, animal fats or both. All three are utilized with both fresh and pre-owned oils.
1. Use the oil just as it is-- typically called SVO fuel (straight vegetable oil);
2. Mix it with kerosene (paraffin) or petroleum diesel fuel, or with biodiesel, or mix it with a solvent, or with fuel;
The first two methods sound simplest, however, as so often in life, it's not quite that easy.
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 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 the majority of, but still unclean enough, many would say. Still, for every gallon of
grease you use, that's one gallon of fossil-fuel conserved, which much less climate-changing carbon in the environment.
People use various mixes, varying from 10% vegetable oil and 90% petro-diesel to 90% grease and 10% petro-diesel. Some people simply utilize it that method, launch and go, without pre-heating it (that makes veg-oil much thinner), or perhaps use 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 a very hard and tolerant motor-- it will not like it however you probably will not eliminate it. Otherwise, it's not smart.
To do it properly you'll need what totals up 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 requirement for the mixes.
Blends with various solvents and/or with unleaded gas are "speculative at finest", little or nothing is learnt about their impacts on the combustion attributes of the fuel or their long-term results on the engine.
Higher viscosity is not the only issue with using vegetable oil as fuel. Veg-oil has different chemical properties and combustion characteristics from the petroleum diesel fuel for which diesel engines and their fuel systems are created.
Diesel motor are state-of-the-art makers with very accurate fuel requirements, especially the more modern-day, cleaner-burning diesels (see The TDI-SVO controversy).
They're tough but they'll just take a lot abuse. There's no guarantee of it, however using a mix of up to 20% veg-oil of great quality is said to be safe enough for older diesels, especially in summer.
Otherwise utilizing veg-oil fuel needs either a professional SVO option or biodiesel. Mixes and blends are typically a poor compromise. But mixes do have an advantage in winter.
As with 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) More about fuel blending and blends.
