API CF-4 Class
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Engine oils for use in four-stroke diesel engines, starting with 1990 model-year engines.
Engine oils of this class can be used in four-stroke diesel engines whose operating conditions involve high-speed regimes. For such conditions the oil-quality requirements exceed the capabilities of the CE class, so CF-4 engine oils can be used in place of CE-class oils (where the engine manufacturer recommends it).
API CF-4 oils must contain suitable additives that reduce oil consumption and protect against deposits in the piston assembly. These engine oils are primarily intended for use in the diesel engines of heavy-duty tractor units and other vehicles used for long highway hauls.
In addition, such engine oils are sometimes given the dual class API CF-4/S. In that case, where the engine manufacturer recommends it, these oils can also be used in petrol engines.