100 Maintenance Replacing Fuel Filters General The filters are an important part of the fuel system. Always replace the filters at the recommended intervals and use the recommended filter types for the best engine operation and service life. A primary fuel filter is located on the outer right, inside front wheel or outer left frame rail, behind the cab. This filter consists of a filter cartridge, a water separation bowl and may have a fuel heater built in. W2003931 The secondary fuel filter is located on the left side, under the engine control unit (ECU) on the D12D. The filter is contained in a disposable cartridge. Note:
Some fuel filters are located on the left hand frame rail, beside the engine. Fuel Filter Change Intervals Filter change intervals should be tied to the oil change intervals. Depending on the oil change intervals and/or the fuel cleanliness, the filters can be changed every or every other oil change. Maximum mileage between fuel filter change is 25,000 miles (40,000 km) or 600 hours. Note: The Fuel Filter for the D12D engine must be “mounted.” Use only fuel within the fuel system to refill filter. This process can be carried out with an electric fuel primer pump.