Shell Helix Diesel HX5 15W-40. a high-quality base oils reduces oil volatility and therefore oil consumption. Good oxidation stability resists oil degradation throughout the oil-change interval. Active Cleansing Technology works harder to protect than mineral oils by continuously preventing soot build-up. Shell Helix Diesel HX5 uses special Active Cleansing Technology to help diesel engines to operate efficiently for a smoother and quieter drive. Soot from diesel combustion can increase an oil^s viscosity, which forces the engine to work harder. Shell Helix Diesel HX5 removes soot from surfaces and reduces the rate of further soot build-up. The oil cleans the engine and continues to flow quickly, so that the engine operates efficiently and smoothly. In independent tests, engine vibration was reduced after a Shell Helix Diesel HX5 oil change