Combinations of Fuels


The presence of gasoline mixed with other onboard fluids significantly reduces the fire point of the other fluids [1]. The graph below shows that even a small amount of gasoline reduces the fire point of power steering fluid. Similar results were found for engine oil and automatic transmission, power steering and brake fluids, and are likely for other onboard fluids as well.


Fire Point of Power Steering Fluid/Gasoline Mixtures


Diesel Fuel Contamination with Gasoline


In another source [2], it was reported that contamination of diesel fuel with 5% gasoline lowered the flashpoint to 90 degrees F below that of pure diesel fuel (from 167 to 77 degrees F). Even a small degree of contamination can therefore reduce the flashpoint of diesel fuel to fuel temperatures expected during normal operation in some parts of the country. However, a contact at the American Petroleum Institute [3] reported that on average, diesel fuel is contaminated with approximately 1 cup of gasoline per 4,000 gallons of diesel fuel; this level of contamination would not be significant.


  1. Ohlemiller, T.J., et al., “Aspects of the Motor Vehicle Fire Threat from Flammable Liquid Spills on a Road Surface,” Building and Fire Research Laboratory, NIST, August 1998.
  2. Mowrer, F.W., et al., “Heavy Truck Fuel System Safety Study: Final Report ,” August, DOT HS 807 484, 1989.
  3. Personal correspondence with API, August 2001.