Surface durability of steel rollers lubricated by fresh and used engine oils in comparison with gear oil

The lubricating oil used for the gasoline engine of passenger cars has been exchanged for a fresh oil after running a distance in the range of 3.000 to 10.000km, in Japan, in most cases. In the present investigation, used engine-oils were obtained by two different methods; (1) the oils were gathered at a car service centre, or (2) produced using test cars and fresh engine oils. The fresh and used engine-oils were chemically analysed and the amounts of nine elements (S, Cl, P, Zn, Pb, Mo, Fe, Al, Ca) in the oils were compared with those of a gear lubricating oil. Using a four ball tester, scoring load for the test oils were measured and then surface durability tests were conducted using a two roller testing machine. Many pits occurred at a Hertzian contact pressure of 1.000MPa on the steel rollers with a hardness of 180HB when a fresh engine-oil or the gear oil was used for lubricating the rollers. However, not a single pit occurred at the same contact pressure up to 10 million rotations when the used engine-oil was used. The reason for the higher surface durability was explained using the results of the chemical analyses and scoring tests.