October 6, 2020

Biodiesels and Cold-Weather Don’t Always Mix

Biodiesel is a renewable, biodegradable fuel used in fuel compression-ignition engines and is manufactured from vegetable oils, animal fats, or recycled cooking grease. Biodiesel is a cleaner-burning fuel and can either be burned in its pure form or blended with conventional diesel fuels.

  • B2: 2% biodiesel mixed with 98% diesel
  • B5: 5% biodiesel mixed with 95% diesel
  • B10: 10% biodiesel mixed with 90% diesel
  • B20: 20% biodiesel mixed with 80% diesel
  • B100: 100% biodiesel mixed with 0% diesel

The Engine Manufacturers Association has indicated that biodiesel use up to B5 should not cause engine or fuel system problems. However, some manufacturers may provide warranty coverage of B20 and higher under specific conditions.

Effects of Cold-Weather on Biodiesels

In the Northern U.S. and Canada, higher blends of biodiesel can create engine performance issues due to poor cold-flow properties. Performance depends on the blend of biodiesel, the feedstock oil, and the petroleum-diesel characteristics. Low blends of biodiesel (i.e. B5) tend to perform more like conventional diesel fuel in cold weather (i.e. regular No. 2 diesel). Both have some compounds that can crystalize in extreme cold. Additionally, a lower saturated fat content generally creates a better cold weather biodiesel.

Higher blend biodiesels, however, will tend to gel (or freeze) more quickly. Essentially, as the temperatures get colder, you’ll notice a loss of power as the fuel gels resulting in clogged filters and plugged fuel lines. Eventually, your engine will shut down.  

Cold-Weather Characteristics

You can measure a diesel fuel’s cold-weather characteristics using a variety of tests including:

  • Viscosity: Measures the resistance to flow at a stated temperature
  • Cloud Point: the temperature at which small, solid crystals are seen as the fuel cools
  • Pour Point: the lowest temperature at which there is movement of the fuel when the container is tipped.
  • Simulated Distillation: Measures fuel volatility over temperature range

Cloud point and pour point testing are often used as an estimate for cold filter plugging point – a fuel could work in an engine if the temperature is below the cloud point but won’t below the pour point. Biodiesel tends to have a much narrower range of temperatures (often a difference of a few degrees) between the cloud point and the pour point.

Other tests that may be useful for monitoring cold weather diesel fuel performance include the Cold Filter Plugging Point (CFPP) or Fatty Acid Methyl Ester (FAME) test.

Fluid Life offers a comprehensive seasonal diesel fuel test package to help validate cold weather performance of your stored diesel fuel.

Improving Performance in Cold Weather

There are several steps you can take to improve cold-weather performance with biodiesels, and conventional diesel fuels.

  1. Seasonal fuel testing: fuels should be tested prior to winter to determine expected performance in cold weather
  2. Use fuel additives: fuel blenders and suppliers fight crystallization by adding a cold flow improver additive
  3. Test for contamination: test bulk storage tanks for water and other contaminants
  4. Prevent water contamination before it starts: good tank maintenance procedures can prevent ingress of water into storage tanks
  5. Keep it warm: a heated garage is the best place to put a diesel vehicle when not in use. If not available, engine block heaters can help keep your engine warm when not running.

High blend biodiesels can cause engine issues in cold-weather climates. To ensure good performance, work with your fuel provider to determine the biodiesel blend appropriate for your weather conditions. In addition, follow maintenance best practices in winter and do routine diesel fuel testing so you can maintain a consistent level of performance.