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An In-Depth Guide On Changing Your Diesel Fuel Filter

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You'd be surprised at what you'd find in a gallon of diesel fuel. While gasoline has its fair share of contaminants, diesel fuel is often chock-full of microorganisms, solidified wax, sediment and other contaminants.

With today's high-pressure common rail fuel injection systems, you can't afford to have these particles damaging or even destroying injectors. For this reason, changing your diesel fuel filter on a regular basis is a crucial maintenance task. The following explains how you can do this on your own, along with a few caveats to avoid along the way.

Locating the Fuel Filter

The first step involves locating the diesel fuel filter. Keep in mind that most diesel vehicles have two of these filters: a primary filter located closest to the fuel tank and fuel pump, and a secondary filter located near the engine. You should consult your owner's manual for a precise location of the diesel fuel filters, since they can vary among vehicles.

Fuel Filter Removal and Replacement

After locating the diesel fuel filter, your next step involves preparing it for draining and removal. Some filters may have sensors attached to the bottom of the housing, so don't forget to unplug the sensors prior to draining and removing the filter. If you're replacing the primary fuel filter, you may have to undo the quick-disconnect fuel lines attached to it.

Next, place a catch pan underneath the filter. Locate the diesel fuel filter's drain valve and open it to drain the excess fuel in the filter. To make things easier and a bit cleaner, you can attach a length of hose with roughly the same diameter as the drain valve outlet and direct the excess fuel into the pan that way.

Afterwards, the actual removal and replacement of the diesel fuel filter can take place. Most modern filters are split between cartridge-style types and sealed units that must be replaced as an entire unit. How you remove these filters depends on your vehicle's specific setup:

  • Some fuel filters are held on with a single nut or bolt, with which you can use a ratchet and the appropriate socket to remove.
  • Others are held in place with plastic clips or snap fasteners. These are the easiest and fastest to remove, although care should be exercised to avoid breaking the clips or fasteners.
  • Some filters may require a specialized tool for removal and installation. It's a good idea to check your owner's manual for more details, since the required tool could vary among manufacturers.

When replacing the filters, don't forget to lubricate and install the new O-rings provided with the filter. Reusing the old O-rings isn't advisable, as these won't provide the proper seal required for the new filter to function without leaks.

Post-Installation Prepwork

After installing the new filters, it's likely you'll have to prime and bleed the fuel system. This step ensures that there aren't any air pockets trapped within the fuel lines. Some diesel vehicles offer a manual primer pump for this purpose – all you'll have to do is pump the primer and crack open the nearby air bleed screw to release the built-up air from the fuel system.

Other vehicles may require the fuel pump to be cycled on and off several times via ignition key without starting the engine. This also allows the fuel system to fill the new filters with fuel and, at the same time, purge excess air from the fuel lines. A select few may require you to crank the engine (without allowing it to fire) in order to prime the fuel system.

After the fuel system is primed and ready, it's a good idea to give it a test drive. Not only should you be on the lookout for any drivability issues (such as fuel starvation) as you drive, but you should also check for fuel leaks after you're done driving.