Short answer
Biodiesel blends are named by percentage: B5 is 5 percent biodiesel, B20 is 20 percent. Pure biodiesel blend stock (B100) is covered by ASTM D6751, blends from B6 to B20 by ASTM D7467, and blends up to B5 are treated as ordinary diesel under ASTM D975. Engine makers set their own limits on which blends they accept.
Three specifications, one fuel chain
ASTM D6751 governs B100, the fatty acid methyl ester made from vegetable oils, animal fats or used cooking oil that is blended into diesel. It is a blend stock specification, not a fuel most engines are meant to run on directly.
ASTM D7467, first published in 2008, covers finished blends of 6 to 20 percent biodiesel in light middle or middle distillate diesel, with S15, S500 and S5000 sulfur grades. The biodiesel portion must meet D6751. Up to 5 percent biodiesel can be blended into No. 1-D or No. 2-D and still be sold as D975 diesel.
Why blends behave differently
Biodiesel has a higher cloud point than typical petroleum diesel, so higher blends can gel sooner in cold weather unless the blend is adjusted for season. It is also more prone to oxidation in storage and holds more dissolved water, which matters for fuel that sits in tanks.
Biodiesel is a good solvent. When a vehicle or tank first switches to a biodiesel blend, it can loosen old deposits, so early fuel filter changes are common during a changeover.
Engine and equipment limits
Engine makers publish the maximum blend their warranties and fuel systems accept. Many on-road diesel engines are approved for up to B20, while some equipment is limited to B5 or less. The owner’s manual or the engine maker’s fuel bulletin is the authority.
Storage and testing
For generators and other equipment where fuel sits for months, biodiesel content affects storage planning. Testing for water, sediment and microbial growth, and keeping tanks full and dry, are standard steps whatever the blend.
Frequently asked questions
Will the pump say if diesel contains biodiesel?
Blends from B6 to B20 are labeled under federal labeling rules. Fuel up to B5 is still D975 diesel and may not be labeled as a blend.
Is renewable diesel the same as biodiesel?
No. Renewable diesel is a hydrotreated hydrocarbon that can meet D975 on its own, while biodiesel is a methyl ester covered by D6751 and blended into diesel.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].
