Caterpillar 1986378 198-6378 FUEL WATER SEPARATOR Advanced High Efficiency Multipack (Pack of 2) Standard Efficiency Fuel Water Separators are designed to eliminate 100% free water and 90% emulsified water along with smaller contaminates while helping extend the life of your secondary filter and expensive injectors. Cat Fuel Water Separators are built to extend the life of your secondary filter and precision fuel system components. Primary vs Secondary: Primary Efficiency Rating: Standard Efficiency