The Cat 1U9891 Diesel Fuel Conditioner with Water Separator is a genuine Caterpillar additive designed to improve fuel quality and protect all Cat diesel engines. This 0.15-liter (5 fl oz) additive acts as a water separator, corrosion inhibitor, detergent, lubricity improver, and stabilizer, treating up to 189 liters (50 gallons) of diesel fuel. It helps prevent fuel system corrosion, keeps injectors clean, and extends engine life.