By Larry Carley
Technical Editor

The fuel filter is often tucked away in a hard-to-find location somewhere under the vehicle or in the back of the engine compartment. Many owner’s manuals no longer list a recommended replacement interval for this filter and some say it’s a “lifetime” filter, which means you don’t have to change it.

The fuel filter is typically located somewhere in the fuel line between the fuel pump and the fuel injection supply rail on the engine. On some late-model Chrysler and Ford vehicles, the filter is located inside the fuel tank and is part of the fuel pump assembly.

The fuel filter’s purpose is to trap dirt and rust particles before they reach the injectors or the fuel pressure regulator. There is also a screen or sock on the fuel pump inlet, but this is only to prevent large chunks of debris (70 to 100 microns in size and larger) in the fuel tank from being sucked into the fuel pump. Most fuel filters will trap particles three microns or larger in size and some will trap particles that are even smaller. And just like air and oil filters, filtering efficiency goes up the dirtier the filter gets. But at the same time, so does the resistance to flow.

A plugged fuel filter is bad news because it causes a drop in fuel flow that chokes off the engine’s fuel supply. A dirty filter may flow enough fuel at idle and low rpm not to cause any noticeable problems, but it may not pass enough fuel at higher engine speeds causing a loss of power and hesitation. If the filter plugs up, it can cause the engine to stall or make it hard to start. Many fuel pumps have been replaced unnecessarily because the real problem was a plugged fuel filter, not a bad pump.

Many experts recommend replacing the fuel filter for preventive maintenance every two to three years or 30,000 miles, or anytime a fuel restriction is suspected. The fuel filter should also be replaced if the fuel pump has failed and is being replaced.