Diesel fuel and other fluids are commonly tested for lubricating ability using a device called a High Frequency Reciprocating Rig (HFRR). HFRR testing is the internationally accepted, standardized method for evaluating a fluid’s lubricity.

During the test, a steel ball bearing moves back and forth at a very high frequency against a metal surface for 90 minutes. Both surfaces are fully immersed in the test fluid (in this case, treated diesel fuel).

After the test is complete, the ball bearing is examined under a microscope and the resulting wear scar is measured in microns. The larger the wear scar, the poorer the lubricating ability of the fluid. Each sample is tested twice by an independent lab, and the final result is the average of both tests.

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HFRR Standards

The current U.S. standard for commercially available diesel fuel requires a wear scar of no greater than 520 microns.

The Engine Manufacturers Association has recommended a stricter standard of 460 microns, which is more consistent with pre-ULSD diesel fuels.

Most experts agree that the 520-micron standard is adequate, but also recognize that lower wear scar values indicate better lubricity and increased protection.

In the comparison chart below, you’ll see how PlanetSafe-GT and PlanetSafe-DT perform against popular fuel additives on the market.

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