Valve train (VT) wear protection has become an increasingly important passenger car engine oil (PCEO) performance feature. Directionally higher levels of valve train wear have been noted with the development and continuous influx of fast-bum (combustion-efficient) engines into the U.S. automotive market in recent years (1979–present). Field testing has been a primary measure of severe engine VT wear performance. This type of testing has become increasingly more expensive, and time consuming, however. There was a need for a short-time, more cost-effective tool to help carry out our experimental work.A real-time Radioactive Marker Technique for measuring VT wear was developed to satisfy this need and to improve our flexibility in optimizing oil chemistry to meet engine VT wear requirements. This real-time technique involves surface layer activation (SLA) of one cam lobe in the engine's valve train with subsequent monitoring of the radioactive surface as wear occurs. The radioactive camshaft is placed in the engine and a motored wear test begun. A detector collects and monitors the emitted radiation as the engine is running. Radiation decreases as wear occurs and this relationship is used to follow the dynamic wear process. This technique allows one to monitor VT wear dynamically, as it occurs in a running engine, without taking the engine apart to physically measure the wear. However, most of today's quality PCEO's do not produce much VT wear over the relatively short (16 hrs) test period and an oil aging chemical, a hydroperoxide, was introduced into the wear test regime to relate better to longer term field service. Under the improved test regime, the oil and engine are first conditioned overnight to expose the engine's valve train to the oil's anti-wear technology, and then the oil-aging chemical is added, at a fixed rate once per hour, while the engine is motored and the wear process continues. The test is continued until a significant (≥1μ/hr) increase in wear rate occurs. The difference in time between the point of significant wear rate increase and the point of initial hydroperoxide addition is designated “The Time to Accelerated Wear”. The larger this number, the better the anti-wear capability of the oil being tested. Data from this Radioactive Marker Engine Test with oil aging suggests a correlation with VT wear observed after long term (50K miles, 8 months) field testing.