Piston ring wear measurements were carried out in a standard production 2.3-liter engine using compression rings that had been subjected to bulk thermal neutron bombardment. As the radioisotopes produced by this process were worn from the rings during each test run, they served as irradiated tracers for the detection of wear particles.A total of 32 tests were conducted on six different oils. All oils showed two distinct types of wear. The first, start-up wear, is characterized by a high wear rate and a relatively short duration. The second, steady-state wear, showed a much lower wear rate and continued in a constant manner for the remainder of the test. The start-up ring wear rate was substantially larger than the steady-state wear rate.The addition of a unique boundary chemistry engine treatment substantially reduced both the total amount of piston ring wear, and the rate at which wear particles were produced during start-up.