Diesel Fuel Filter

The diesel fuel filter is located in the engine compartment, in the fuel line, before the injection pump. The basic filter is shown in Fig. 5-7. For information on draining water from the diesel fuel filter, see 5.8 Diesel Fuel Water Separator.

Fig. 5-7.

Diesel fuel filter installed in engine compartment. Small arrows, indicating direction of fuel flow, should point to front of engine compartment. A is supply line from fuel tank. B is outlet line to diesel injection pump. C is vent screw, used when draining water from filter. Drain screw is at bottom of filter (not shown).

On 1988 and later models with pre-warmed diesel fuel filters, a temperature-sensitive control valve at the top of the filter allows excess diesel fuel warmed by the injector pump to be recirculated through the filter. This keeps the fuel warm and prevents the fuel separation and wax buildup which is common at low temperatures. The control valve opens whenever the temperature drops below 32°F (0°C), and closes after the temperature of the fuel is above 50°F (10°C). The fuel line and control valve connections for the pre-warmed diesel fuel filter are shown in Fig. 5-8.

Fig. 5-8.

Pre-warmed diesel fuel filter seen from above. Control valve is removed/replaced by removing retaining clip and sealing O-ring underneath.

When replacing the filter, disconnect the battery negative (-) terminal, then remove the two hoses at the top of the filter. On pre-warmed filters with the control valve, leave the two fuel return lines connected and remove the control valve by removing the retainer clip. Remove the bracket with the filter, then remove the filter.

Install the fuel hoses on the new filter, making sure that they are routed as shown. Torque the bracket mounting nuts to 25 Nm (18 ft. lb.). When installing the control valve on a prewarmed type filter, use a new O-ring. Install the valve carefully to prevent damage. A damaged control valve will allow the engine to start but will not deliver any more fuel.