C7 Industrial Engine Operation and Maintenance Manual – Fuel System Primary Filter (Water Separator) Element – Replace

Water in the fuel can cause the engine to run rough. Water in the fuel may cause an electronic unit injector to fail. If the fuel has been contaminated with water, the element should be changed before the regularly scheduled interval.

The primary filter/water separator also provides filtration in order to help extend the life of the secondary fuel filter. The element should be changed regularly. If a vacuum gauge is installed, the primary filter/water separator should be changed at 50 to 70 kPa (15 to 20 inches hg).

Replace the Element

  1. Close the main fuel supply valve.

Typical primary fuel filter/water separator

(1) Primary fuel filter element

(2) Collection bowl for the water separator

(3) Drain for the water separator


  1. Remove the element from the element mounting base while the bowl is attached.


  1. Dispose of the fuel in the fuel filter element. Remove the bowl from the element . The bowl is reusable. Do not discard the bowl. Dispose of the used element.


  1. Remove the O-ring from the bowl. Clean the following components: 
    • Bowl 
    • O-ring 
    • Mounting base 

    Inspect the O-ring for damage and for deterioration. Replace the O-ring, if necessary.


The primary filter/water separator may be prefilled with fuel to avoid rough running/stalling of the engine due to air. Do not fill the secondary filter with fuel before installation. The fuel would not be filtered and could be contaminated. Contaminated fuel will cause accelerated wear to fuel system parts.


  1. Lubricate the O-ring with clean diesel fuel. The element may be filled with fuel at this time.


  1. Install the bowl on a new element. Tighten the bowl by hand. Do not use tools in order to tighten the bowl.


The water separator is under suction during normal engine operation. Ensure that the vent plug is tightened securely to help prevent air from entering the fuel system.


  1. Open the main fuel supply valve.


  1. Start the engine and check for leaks. Run the engine for 1 minute. Stop the engine and check for leaks again.Detection of leaks is difficult while the engine is running. The primary filter/water separator is under suction. A leak will allow air to enter the fuel. The air in the fuel can cause low power due to aeration of the fuel. If air enters the fuel, check the components for overtightening or under tightening.
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