What biodiesel is

The Alternative Fuels Data Center (AFDC) describes biodiesel as a renewable, biodegradable fuel manufactured domestically from vegetable oils, animal fats or recycled restaurant grease. In its unblended form it is called B100, pure or neat biodiesel. Like petroleum diesel, it fuels compression-ignition engines.

Fueleconomy.gov adds an important warning: never fuel a vehicle with grease or vegetable oil that has not been converted to biodiesel, because it will damage the engine.

From Biodiesel Fuel Basics (Alternative Fuels Data Center) and Biodiesel (fueleconomy.gov), read November 9, 2026.

Biodiesel blends: B5, B20 and B100

The number after the "B" is the percentage of biodiesel. Here is how the AFDC and fueleconomy.gov describe the common blends:

From Biodiesel Blends (Alternative Fuels Data Center), Biodiesel Benefits and Considerations (Alternative Fuels Data Center) and Biodiesel (fueleconomy.gov), read November 9, 2026.

The AFDC says engines on B20 have similar fuel consumption, horsepower and torque to petroleum diesel; B20 has 1% to 2% less energy per gallon, and many B20 users notice no difference. Fueleconomy.gov puts the drop in fuel economy and power at about 2% for B20 and 10% for B100.

Can my diesel car or truck use biodiesel?

Check first. Fueleconomy.gov says most automakers approve blends up to B5 and some approve blends up to B20, and that using the wrong blend could damage the engine or void the manufacturer's warranty. The AFDC likewise advises checking your engine maker's recommendations and warranty statement before using biodiesel.

Low-level blends such as B5 are ASTM-approved for safe operation in any compression-ignition engine designed to run on petroleum diesel, including light- and heavy-duty diesel cars and trucks.

If you switch to a high-level blend, the AFDC notes that B100 has a solvent effect: it can loosen deposits left by petroleum diesel, which may clog fuel filters in the first few tanks. High-level blends can also affect engine warranties and gel in cold temperatures.

From Biodiesel (fueleconomy.gov), Biodiesel Blends (Alternative Fuels Data Center) and Biodiesel Benefits and Considerations (Alternative Fuels Data Center), read November 9, 2026.

Biodiesel in cold weather

Cold-weather performance depends on the blend, the feedstock and the petroleum diesel it is mixed with. In general, the AFDC says, smaller percentages of biodiesel perform better in the cold, and No. 2 diesel and B5 typically perform about the same. Both biodiesel and No. 2 diesel contain compounds that crystallize in very cold temperatures, so fuel suppliers add cold flow improvers in winter.

Fueleconomy.gov notes that B100 is generally not suitable for use in low temperatures. For Illinois winters, follow your owner's manual and see our guide on how to winterize your car.

From Biodiesel Fuel Basics (Alternative Fuels Data Center) and Biodiesel (fueleconomy.gov), read November 9, 2026.

Biodiesel vs. renewable diesel

The AFDC stresses that renewable diesel and biodiesel are not the same fuel:

From Renewable Diesel (Alternative Fuels Data Center), Biodiesel Fuel Basics (Alternative Fuels Data Center) and Biodiesel (fueleconomy.gov), read November 9, 2026.

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