API has developed two visually different API Service Symbol Donuts so that consumers can distinguish between the two new categories of oils. Image: API The American Petroleum Institute's new diesel engine oil-service categories, API CK-4 and FA-4, will begin appearing in the marketplace on December 1. New API Donuts denoting the categories will appear on licensed products and marketing materials allowing consumers to identify oils meeting CK-4 or FA-4, which are expected to be recommended in new owner's manuals and by engine manufacturers.
