DIY: Replacing Your Fuel Filter

   DANGER: Gasoline is poisonous, does not taste very good and may burn sensitive lips. So don't hold the filter to your mouth to blow through it. Instead, attach a short piece of clean rubber hose to the filter and then blow through the hose to test the filter.

   Clogged Filter Problems:
A completely plugged fuel filter will stop your engine cold by choking off the flow of fuel to the carburetor or injectors. The engine may not start, or it may start, then stall and die. It's not only important to have good fuel pressure, but you also need a good volume of fuel. In fact there is a specification for the volume of fuel in a given time, usually 1.8 to 2.7 quarts per minute.

   Some filters have a bypass valve built into them, however that will allow fuel to bypass the filter element if it becomes clogged. Fuel continues to flow, but it will carry dirt to the carburetor or injectors, which can create additional problems.

   In-Tank Filters:
Inside the fuel tank, attached to the fuel pickup tube is a mesh sock or screen that is a pre-filter. This sock prevents large pieces of rust and dirt from being sucked into the fuel pump. If this sock or screen becomes plugged with dirt or other debris, it will have the same effect as a clogged fuel filter. So, if you've are experiencing a fuel deprivation problem and have replaced the fuel filter with no effect, you could very well have a clogged fuel pump sock or screen. In most vehicles this will require the removal of the fuel tank.

   Replacing The Fuel Filter:
Replacing the fuel filter periodically, once a year or so, for preventative maintenance will greatly reduce the chances of fuel filter related problems. Most carmakers today no longer specify a replacement interval for the fuel filter. And those that do specify a replacement interval, it is a very long interval, like once every five years or 50,000 miles. A lot of Technicians, myself included, feel this is unrealistic. If you wait that long to change the fuel filter; you are just asking for trouble. More so if you live in the country and drive on gravel or dirt roads, buy the cheapest gas you can from off-brand stations, use gas with alcohol in it, or your vehicle is more than six or seven years old and may have rust in the tank.

   The fuel filter on carbureted engines is usually located at the inlet fitting, Figure 1, of the carburetor, or an "in-line" filter, Figure 2, is used between the fuel pump and carburetor.

   When you replace an in carburetor fuel filter care must be taken to not cross thread the fitting or over tighten the fitting. The threads in the carburetor are relatively soft and can be damaged easily. Make sure it is tight enough not to leak, but that's it. You can use a dab of sealer or Teflon® tape to help the seal.

   If you use Teflon® tape, don't use too much because the excess could get inside the carburetor and block internal passages. Do not use any type of RTV silicone sealer because gasoline will dissolve it away.

   Most new fuel filters come with two new rubber hoses that go on either side of the fuel filter and connect to the metal fuel lines on the vehicle. Use the new hoses and throw out the ones. Rubber hoses do deteriorate and can leak, causing a potentially dangerous situation. Leaking fuel in the presence of an ignition source could lead to a fire. In addition, make sure the hose clamps are positioned properly and tighten to specifications.

   NOTE: Most in-line fuel filters have an arrow showing the direction fuel should flow through the fuel filter. Install the fuel filter so the arrow points toward the carburetor.

   Fuel Injection Filters:
Fuel Filters on fuel-injected vehicles are larger, are encased in a metal container and have a finer filter element, to protect the fuel injectors, than fuel filters on carbureted engines. And they are also more expensive to replace.

   CAUTION: Fuel injected engines have fuel under high pressure in the fuel lines. Even if the vehicle has been sitting without being started for a day or two, there will still be pressure in the fuel system. Follow the manufacturer's procedure for relieving fuel pressure before you remove the fuel filter. Usually removing the fuel pump fuse or fuel pump relay and cranking the engine will relieve most of the fuel pressure.

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