Biodiesel blends are widely used, especially in farm country, and most modern diesels can run on common blends without trouble, provided the fuel meets its specification, the blend level is approved by the engine maker, and the fuel is stored and handled properly. Under the ASTM specifications, conventional diesel fuel (ASTM D975) can contain up to 5% biodiesel, while blends from 6% to 20% (B6 to B20) are covered by a separate specification, ASTM D7467. The fuel injection issues associated with biodiesel come mainly from its cleaning effect on dirty systems, cold-weather behavior, storage stability and water, not from the blend itself when it’s on spec. (DieselNet: US biodiesel fuel standards)
What the blend numbers mean
- B5 or less: may be sold as ordinary diesel fuel under D975, without separate labeling. You may already be using it.
- B6 to B20: covered by D7467.
- B100: pure biodiesel, specified under ASTM D6751 as a blending component.
Engine makers specify which blend levels their engines are approved for. Check your owner’s manual or engine maker’s guidance, especially for higher blends and during warranty.
How biodiesel affects the fuel system
It cleans
Biodiesel is a good solvent. In a tank and fuel system that have run on petroleum diesel for years, a first switch to biodiesel can loosen deposits and sediment that then collect in the fuel filters. Plugged filters soon after a switch are common, especially when moving to higher blends such as B20. Plan for an early filter change.
It has poorer cold flow
Biodiesel typically has a higher cloud point than petroleum diesel, so blends can gel or plug filters at higher temperatures. Fuel suppliers adjust winter blends accordingly. In cold weather, make sure the fuel in your tank is suitable for the temperatures you’ll see. See diesel won’t start in cold weather.
It’s less stable in storage
Biodiesel blends oxidize more readily than petroleum diesel and can form deposits and acids over long storage. A canceled military specification for B20 advised against storing blends longer than six months from manufacture. For seasonal equipment and standby engines, fuel turnover matters.
It holds more water
Biodiesel can hold more dissolved water than petroleum diesel, and water supports microbial growth. Tank and filter maintenance matter even more. See farm diesel fuel storage tanks.
Seals and materials
Older engines with fuel system seals and hoses made from some elastomers may be affected by higher biodiesel blends, particularly B100. Modern engines generally use compatible materials.
Injector deposits
Off-spec biodiesel, with contaminants or impurities, has been associated with deposits that can affect high-pressure injectors. Buying fuel that meets specification from reputable suppliers is the best protection.
Best practices for using blends
- Use blends your engine maker approves.
- Buy from suppliers who sell fuel that meets ASTM specifications.
- Change fuel filters early after switching to biodiesel.
- Manage storage time, especially for seasonal and standby equipment.
- Keep tanks dry and check regularly for water and microbial growth.
- Pay attention to winter blends and cold-flow properties.
Quick answers on biodiesel
Is B20 safe in my common-rail truck?
It depends on your engine maker’s approval. Many engines are approved for blends up to B20, but not all are, and some approvals carry conditions. Check your owner’s manual.
Does biodiesel gel?
Biodiesel blends generally have poorer cold-flow properties than petroleum diesel. Suppliers adjust blends for winter, but it’s worth confirming what’s in your tank before cold weather.
Will biodiesel clean my injectors?
Its solvency can loosen deposits in tanks and lines, which is why filters can plug after a switch. It isn’t a substitute for testing injectors that are already causing problems.
Further technical reference: Bosch Mobility: common-rail system overview. Use the exact engine/injector/pump service information for applicable procedures and limits.
When symptoms show up
Plugged filters, rough running or hard starting after a switch to biodiesel usually point to loosened deposits, storage problems or cold flow rather than injection component failure. If symptoms persist after filters and fuel quality are addressed, test the injection system. Diesel Control Technicians tests and repairs injection pumps and injectors for farm, fleet and automotive engines. Bring components to our Hutchinson shop or Great Bend satellite office, or ship them to DCT.
After the safety or contamination issue is assessed: Ask DCT about supported component service with the exact part number and findings; a bench result cannot replace the engine maker’s complete repair requirements.