Using R-99 or R-95 Diesel Fuel

GM Engineering has recently approved the use of renewable diesel, R-99 or R-95, for all 2006-2022 GM vehicles equipped with a diesel engine. (Fig. 25)


Fig. 25


Renewable diesel (RD) is essentially any diesel fuel produced from a renewable feedstock, such as recyclable vegetable oil, that is predominantly hydrocarbon (not oxygenates) and meets the requirements for use in a diesel engine. Renewable diesel is chemically identical to Ultra-Low Sulfur Diesel (ULSD) fuel and can be blended in volume ratios of 1 to 99% with ULSD diesel fuel.

Renewable diesel is not the same a biodiesel. B20 diesel fuel is a blend of up to 20% bio components and 80% conventional diesel.

Regular diesel fuel and renewable diesel must meet ASTM D975 diesel fuel standards. Renewable or Biomass fuels have an API (a measure of the fuel specific gravity or density) of up to 50. The API can be between 40 and 50, depending on if the fuel is a combination of #1, #2, and the R-99/95 fuel. Renewable diesel fuel is also clear in color when not mixed with other fuels.

Currently, there are four things to examine when testing fuel:

  • Look at the color of the fuel compared to what is normally seen in your region. Cloudy looking fuel is an indication that there may be an issue with the fuel.
  • Look for any separation of the fuel, which can be anything from sediment settling or different layers, like water, being seen.
  • Check the Specific Gravity (API) of the fuel.
  • Check for contamination. Take a sample of the fuel and put it in a Styrofoam cup. Place the cup in a drain pan. Fuel contaminated with gasoline will certainly melt the cup within half an hour. B20 Biodiesel will also melt the Styrofoam cup, but it will take about an hour.

For more information, refer to #PIP5856.


– Thanks to Steven Ulch

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One Comment

  1. how much of difference is there between a R99 vs R95 renewable diesel? Please explain because unocal 76 was R99 but now R95, is it to cut cost? Is R99 a tiny bit better than R95? Thank you.

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