Fuel filters clean fuel and protect fuel injectors. Good maintenance has always dictated replacing fuel filters at regular intervals. Today they are disappearing from maintenance schedules and the under side of vehicles.

Many car and truck owners have replaced their own fuel filters over the years. Just look under the vehicle, follow the fuel lines and there it was. The Chevrolet Silverado, Tahoe, Suburban, Avalanche and GMC Sierra and Yukon are very popular vehicles. Until 2003 the fuel filter was replaceable.

Look for the fuel filter on a 2004 or newer model and you may be surprised. These vehicles and millions of others, no longer have an external fuel filter. Instead the fuel filter has been moved inside the fuel tank. On the GM truck and SUV models mentioned the fuel filter is available only with a new fuel pump.

Today many manufacturers are placing the fuel filter inside the fuel tank. This move cuts assembly-line time and removes possible warranty problems. Fuel tank mounted filters are nothing new. Many vehicles have used them for years.

Most in-tank fuel filters are considerably larger than their external counterparts. In theory, they should give many years of service. For instance Toyota, Honda and Nissan in-tank fuel filters usually last at least 100,000 miles. Fortunately, these cars have access panels and the fuel filter is sold separately. About an hour is normally required to remove the seat, access panel, fuel pump and replace the filter. Without this access panel, the fuel tank has to be removed, as on the GM vehicles mentioned above.

Cutting a fuel filter open reveals a simple design. A pleated material serves as the filter. Fuel enters the housing and flows around and through the filter, trapping debris between the filter and the housing. Clean fuel then flows out of the filter and to the engine. If the filter did not trap the inevitable debris, the fuel injectors would soon be clogged.

As the fuel filter does its job, the element becomes restricted. This reduces the amount of fuel that can flow through. If the filter restricts too much fuel, the fuel pump will not be able to provide enough pressure to the injectors.

Loss of power and cutting out under load are symptoms of a clogged fuel filter

One typical example of fuel filter restriction is a vehicle that starts to cut out or lose power driving up an incline, such as a bridge. Under load, fuel demand increases and a clogged fuel filter blocks the needed flow.  As the fuel filter gets dirty, the fuel pump has to work much harder.  A restricted filter may also damage the fuel pump.

A fuel pressure test is very handy in determining fuel filter restriction. A technician may also use a digital lab scope to observe the fuel pump wave-pattern.

Years ago, many fuel filters were held in place by hose clamps. This is NOT the case today. Vintage fuel systems operated around five to ten PSI of pressure. Modern fuel systems often have ten-times that pressure. Though the fittings may appear similar, a modern snap-type fitting is NOT replaceable by a fuel clamp. If the fuel line is damage, the fitting has to be replaced with the proper type or the fuel line has to be replaced.

Snap-together fuel fittings require several types of special tools to remove, depending on their style. Several varieties are in common use and each has a tool of its own. With the proper tool, the retainer is released and the fuel line comes loose from the filter. The new filter is simply snapped back together with the high-pressure fitting. These fittings give very good service and rarely leak, but do require special handling and tools.

Like most things on modern vehicles, fuel filters today are different from those of the past. Being familiar with the type used on the vehicle and having the right tools makes the job easy and safe.

Many top technicians, will cut old fuel filters open as a diagnostic procedure

Viewing the condition and contaminants inside the fuel filter tells a lot about the condition of the fuel system. Rust and moisture suggest the need to remove the fuel tank to inspect for problems. Ignoring this step can result in repeated fuel system problems, damage to fuel pumps and fuel injectors.

The quality of the fuel used has a great affect on fuel filter life.  Dirty or water contaminated fuel can quickly ruin a fuel filter.  Using clean, high quality gasoline will greatly extend the life.  Most in-line fuel filters are recommended for replacement around 45,000 to 60,000 miles. Most in-tank fuel filters will last 100,000 miles or more.