Ruta High Mileage Plus 25W-50 is a high-performance diesel engine oil developed for high-mileage vehicles (75,000 miles or more) and operating in severe conditions. Poor fuel quality, heavy traffic, harsh weather conditions can cause the build-up of a thick, tar-like substance called sludge (Soot). The engine oil is formulated with highly refined base oils and a selected additive package to minimize the development of deposits or sludge (Soot) and therefore the engine will operate at best performance.