Most diesels feature two filters – a primary filter between the tank and transfer pump and another near the engine that gives one final clean before entering their injection systems. Replacing either filter can be easily accomplished similar to changing an oil filter.

Pump

Diesel fuel filters are designed to remove debris and contaminants from working diesel fuel, such as particulates and water. After passing through the filter, any impurities are separated out and sent on their way back towards engines via fuel pumps.

Diesel engines typically utilize two fuel filters: one between the tank and engine to clean fuel before going through a fuel transfer pump; and a secondary filter near injectors which provides one final cleaning before passing through injectors. Both filters should be properly primed.

Most diesel vehicles feature a manual primer pump to quickly bleed out any air bubbles in their system and prim it for starting. Instead of cranking, which wears down batteries quickly, simply pumping until a hissing noise signals all air has been released and you are ready to replace the filter and start your engine.

Bleed

When replacing a diesel fuel filter, the system must be bled to remove air bubbles and primed with new diesel supply. Cranking the engine can help, but can wear down its starter as well as waste fuel; many diesels therefore come equipped with manual primer pumps and air-bleed screws for this purpose.

After taking off the T-handle, carefully place the old filter into a plastic zippered bag for disposal. Unscrew and open the petcock on the bottom of the filter in order to drain any excess water or debris into a clean receptacle.

Once the filter has been taken apart, replace its metal retaining clip that secures its inlet/fuel preheater assembly onto it with another one made of metal or plastic if possible. Reattach the hose, pump your hand-pump until no air bubbles come through the bleed nipple and close/remove hose depending on where bleeder is situated in engine bay – this process could become messy depending where your bleeder resides in engine bay!

Fill

A diesel fuel filter contains fibers designed to catch impurities in the gas and then pass it along to fuel injectors for cleansing. If the filter becomes empty or clogged, your vehicle may be difficult to start, with its injectors wearing out prematurely and injector wear becoming an issue.

If you’re installing a screw-on filter, many models come equipped with plugs to simplify pre-filling the filter. Otherwise, a flathead screwdriver can help separate it from its cap before cleaning its sealing surface with damp cloth before installing its O-ring and your new filter.

Reinstall the hose clamp or threaded bolt to secure the filter to its housing, before hand tightening the cap according to manufacturer’s specification, using either a torque wrench if necessary, pliers, or spring clamp pliers as appropriate. Be mindful not to overtighten, as overdoing it may cause leaks; also consider using Dexron I or

II oil additive, Marvel Mystery Oil or another synthetic diesel lubricant such as Dexron G or other diesel additive to lubricate O-rings for better sealability and improve sealability.

Test

There are various methods available to you for testing whether or not a diesel fuel filter is clogged or restricted, although blowing into some filters makes the job simpler (use an old towel as you may get wet from fuel spillage).

Install the new fuel filter and cycle the key on and off several times until a hissing sound indicates air is leaving your system as it travels through your fuel pump.

One last option would be to purchase a kit from B3C Fuel Solutions that contains four tests in one for diesel fuel oxidation, water content, rust/scale content and sludge/asphaltenes levels. These kits are easy and straightforward ways to ensure that your diesel is meeting its specification all year long.