What is the fuel filter and how does it work?
The fuel filter is made of cellulose or synthetic-based filter media that traps extremely tiny contaminants, such as rust particles and dirt, present in the fuel as it flows from the fuel tank to the fuel injectors. The filter media is sealed within a cylindrical shaped housing that looks like a tiny soda can. You will most often find the fuel filter plumbed into the high-pressure fuel supply line beneath the car, right next to a sturdy frame rail. Some fuel filters, particularly on diesel-powered vehicles, have water traps as well. Some newer cars do not have serviceable fuel filters as the filter is built into the fuel pump located in the fuel tank.
When to consider replacing the fuel filter:
- Scheduled maintenance. The most common reason to change the fuel filter — your vehicle’s maintenance schedule may specify a filter change interval.
- Fuel contamination. If any foreign fluids, bad fuel, or water enters into the fuel system mistakenly, the fuel filter should be replaced.
- Fuel system repairs. If the fuel pump has been replaced, work has been performed on or in the gas tank, or the fuel injectors have been cleaned or replaced, always install a new fuel filter. Major engine repairs, or engine replacement, also require a new filter.
- Leaks. There should be zero leakage of fuel, whether liquid or vapor, in the fuel system. Leaks at the fuel filter connections might necessitate not only a new fuel filter but also new O-rings in the push-on connections to the fuel filter.
- Warning light indication. Diesel powered vehicles may be equipped with a water-sensor warning light circuit to signal the driver if excessive water has accumulated in the fuel filter. The water will have to be drained and the filter possibly serviced or replaced.
How do mechanics replace the fuel filter?
- A clogged fuel filter that is integral to the fuel pump must be removed with the fuel pump from the fuel tank to perform service.
- For all other vehicles, the procedure begins with raising the vehicle and supporting it with steel jack stands.
- The fuel system is depressurized so the filter can be removed from the high-pressure fuel line without gas spraying out.
- The in-and-out connectors to the filter are removed and the filter is removed from the fuel line.
- The new filter is installed using a small amount of oil on the O-rings to ease re-installation of the quick connect fittings. The fuel system is then checked for leaks while the engine is running.
Is it safe to drive with a fuel filter problem?
Yes, so long as the fuel filter is not leaking. If there is a leak, have it repaired before driving the car. If clogging is suspected and potentially causing engine operating problems, have the cause investigated and resolved at your earliest convenience. In extreme cases, a very old filter that may be plugged could disintegrate, allowing what were trapped contaminants to reach the fuel injectors and causing additional problems.
When replacing the fuel filter keep in mind:
- A plugged fuel filter can be ruled out using pressure and volume tests on the fuel system. Given enough elapsed mileage though, all fuel filter replacements should be done as basic maintenance, and so complicated tests are not necessary if the filter is already known to be old.
- Consult the vehicle maintenance schedule to determine when to replace the fuel filter.
- If you have bought contaminated gas, once all fuel system repairs are made, always install a new filter.
- Gasoline is perishable and will eventually degrade into compounds that will damage the fuel system. Generally, if a car has sat unused with gas in the tank for more than 3 to 6 months, the gas should be drained and the fuel filter replaced.