How to Replace a Fuel Filter

an old fuel filter
This in-line fuel filter protects the fuel injectors from damaging contamination.

Kypros / Getty Images

Your car's fuel filter is designed to capture contaminants and prevent them from flowing through the fuel system. Fuel filters are particularly critical for the proper operation and lifespan of high-pressure fuel pump (HPFP), such as those used on gasoline direct injection (GDI) and diesel engines.

The fuel filter is an oft-forgotten aspect of car maintenance. Read on to learn how to replace your own fuel filter and restore full fuel flow for better performance and fuel economy.

How the Fuel Filter Works

Fuel filters are two-stage filters, but the stages aren’t always integrated in the same housing. The first stage fuel filter is usually a metal mesh or fiber medium, able to filter out contaminants on the order of 100 µm (microns: 1/1,000th-mm or 0.00004-in), about twice the thickness of a hair. Under normal circumstances, the pre-filter will last the life of the vehicle, about 250,000 miles or so, but a contaminated batch of fuel might clog it in a single tank. Depending on the vehicle, the second-stage fuel filter change interval may range anywhere from 20,000 miles to 150,000 miles.

macro shot of fuel injector spray
The fuel filter keeps this fuel injector spray well-defined for better engine performance and fuel economy. US DOT / Flickr

The second stage fuel filter is where things get serious in terms of filtration levels and efficiency. Fuel filters can be rated by screen size, capacity, and flow rate. A 40-µm fuel filter should capture more than 98.7 percent of particles larger than 40 microns, about the size of dust you can barely see. This is about the maximum particle you could run through an electronic fuel injection (EFI) port-injection fuel injector orifice between 100 µm and 150 µm. Diesel and GDI HPFPs are more sensitive to fuel contaminants, and so are protected by fuel filters as low as 2 µm, about the size of a bacteria. This is good protection for HPFP passageways and fuel injector orifices as small as 50 µm.

paper filter media
Inside, the fuel filter might feature paper or synthetic media to trap contaminants. Wizmo / Wikimedia Commons

How to Replace a Fuel Filter

The first step in replacing a fuel filter is identifying where the fuel filter is located. Some vehicles use an in-tank fuel filter, while others use in-line filters or cartridge filters. In-line fuel filters might be located anywhere between the fuel tank and the fuel injectors—they can be under the vehicle, along the frame, or mounted on the firewall or elsewhere in the engine bay. Cartridge fuel filters are usually mounted on the engine, firewall, or somewhere solid in the engine bay.

In-tank fuel filters are designed to last the life of the vehicle and aren’t meant to be easily-serviced. Replacing an in-tank fuel filter usually requires removal of the fuel tank or accessing it via the floor panel in the car. On the other hand, in-line and cartridge filters are indeed meant to be serviced and should be regularly. Fuel contamination or fuel filter deterioration may require you to replace the fuel filter sooner, though. Replacing a fuel filter is usually a simple process, if you can easily access it.

First, you need to relieve the pressure in the fuel system. You can do this by removing the fuel pump fuse or relay or by unplugging the fuel pump. Then, run the engine until it begins to sputter, though you don’t have to run it until it totally dies. Shut the vehicle off, remove the key, and disconnect the ground cable from the battery negative (—) terminal.

Then, pack some rags under the fuel filter or put a drip pan under it. It’s best to work in a well-ventilated area to prevent the accumulation of fuel vapors. It’s also a good idea to have a dry-chemical fire extinguisher close at hand, just in case of ignition. Obviously, don’t smoke while replacing a fuel filter.

Compare your new fuel filter with the old, noting fuel flow direction, usually indicated by a painted or stamped arrow. It may be helpful to mark the fuel line and new fuel filter to make installation easier. Now, remove the old fuel filter. Before disconnecting the fuel lines from the fuel filter, remove or disconnect any holding hardware, such as straps or brackets.

an in-line fuel filter
This in-line fuel filter, under the bed of a pickup truck, requires a special tool to disconnect the fuel lines. drivermag / Flickr

In-line fuel filters might be simply hose-clamped, which are easy enough to remove and slip off. Use a twisting motion to break the bond between hose and filter for removal. Special tools might also be required to disconnect an in-line fuel filter.

Union-bolt or banjo-bolt filters require wrenches to disconnect them. Use wrenches in pairs to prevent twisting and damaging the fuel line.

Cartridge filters come in two types. Spin-on filters can be removed with a special tool or band-wrench. Replaceable-media types are similar, but only require you to replace the filter media inside. It’s a good idea to replace the O-ring at the same time.

a spin-on fuel filter
Spin-on fuel filters look and function similar to engine oil filters. Douglas Sacha / Getty Images

Finally, once you’ve removed the old fuel filter, fit the new one in its place and clean the area. Installation is basically the same as removal. At this point, you can reconnect the fuel pump or reinstall the fuel pump fuse or relay. Turn the key on, but do not start the engine yet. Some vehicles will power the fuel pump a few seconds, and you can use this small amount of pressure to check your new fuel pump connections for leaks.

If you don’t notice any leaks, go ahead and start the engine. The engine may not start immediately, since the fuel system needs to refill, but it should start within a few seconds. Recheck for leaks. Some vehicles may set diagnostic trouble codes (DTC) related to fuel pressure or misfire, since you disabled the fuel pump, so use a scan tool to reset the DTCs.

As you can see, replacing a fuel filter isn’t especially complicated and can do your engine a whole lot of good. Aside from protecting the fuel system from contamination, a fresh fuel filter restores full fuel flow for better performance and fuel economy. By doing it yourself, you can also save yourself a bit of money at the auto repair shop.