While the shelf life for #2 diesel is twelve to eighteen months, the shelf life for biodiesel that has not been treated with preservatives is no more than six months in optimal conditions. Not only does biodiesel separate and congeal as it ages, it is also especially susceptible to degradation caused by various environmental factors. When a biofuel mixes with oxygen, for example, sediment can form, which can damage a unit’s fuel system. Biofuels made from unsaturated fats (i.e. vegetable oils) are particularly vulnerable to oxidation. Biodiesel is also hydrophilic, and as it accumulates water from the air or from condensation inside the delivery system, it creates acid that can damage the fuel’s storage container. Finally, heat and sunlight can expedite biofuel degradation.
If degraded fuel is run through an engine, filter plugging, injector problems, sticking or breaking piston rings, and engine lubricant degradation can occur. While the shelf life of biodiesel can be increased with additives and fuel enhancers, biodiesel that has begun to degrade cannot be remedied and should be disposed of.