There are many methods for testing the lubricity of oils . . . each is used for a different purpose. Some tests are good for gear oils, some are good for testing cutting oils, and others are best for testing engine oils. S. M. Hsu and R. S. Gates of the National Bureau of Standards published several papers showing that the 4-Ball Test correlates with engine oil performance.1

The 4-Ball wear-test method is used to determine the relative wear-preventing properties of lubricants in sliding steel-on-steel applications.

In the 4-Ball Test, three ½” (12.7-mm) diameter steel balls are clamped together and covered with the lubricant to be evaluated. A fourth ½” diameter steel ball, referred to as the top ball, is pressed with a force of 40 kgf (392 N) into the cavity formed by the three clamped balls for a three-point contact. The temperature of the lubricating grease specimen is regulated at 75°C (167°F) and the top ball is rotated at 1200 rpm for 60 minutes. Lubricants are compared by using the average size of the scar diameters worn on the three lower clamped balls.

Ball scar measurements and the subtle self-generated frictional heat created by this test are the two best measures of lubrication qualities. One downfall to the ASTM 4-Ball Test is the inability to capture and data log the time versus temperature changes.

 The top ball is rapidly rotated on top of the three lower balls in order to measure scar diameters.

Fluoramics tested Tufoil for Engines using the 4-Ball Test. The test was comprised of three sections: 1) testing only the host oil of Mobil 1; 2) testing only Tufoil; and 3) testing Tufoil when used as an oil additive at a 90% oil/10% Tufoil ratio. When analyzing test results of oil additives, the lower the coefficient of friction, the better. In the test below, you’ll see that adding Tufoil as an engine additive drastically changed the coefficient of friction of the host oil (Mobil 1).

Results of 4-Ball Testing using Tufoil for Engines

The important thing to note on each trend line:

  • 100% Tufoil stabilized and plateaued at a Cof 0.051 at 240 kgf
  • Mobil 1 0w-30 Advanced Fuel Economy climbed a positive slope to CoF 0.122  at 160 kgf
  • Mobil 1 + 10% Tufoil stabilized and plateaued at CoF 0.071 at 150 kgf

Ball to Ball scar diameter was the greatest on Mobil 1 and the lowest on Tufoil and on Mobil 1 + Tufoil.

1 Richard S. Gates, Stephen M. Hsu, “Development of a Four-Ball Wear Test Procedure to Evaluate Automotive Lubricating Oils,” Lubrication Engineering 39(9):561-569· September 1983