A diesel engine fuel filter is used to keep impurities out of the diesel engine. Possible impurities include moisture and other foreign particles in the diesel that are not intended to be in the engine. By removing moisture and other undesirable elements, the diesel filter helps reduce wear and tear thus increasing the engine’s life.

It also reduces clogging in the engine and therefore increases engine performance. Despite there being over 50 different types of diesel engines, fuel filters and lift pumps are still an integral part of each and every one of these diesel fuel systems.

How Do Diesel Fuel Filters Work?

A fuel filter for diesel is comprised of two filters, the primary filter and secondary filter. The primary filter is capable of riding the engine of larger dirt particles of up to 30 microns. Secondary pumps typically filter the smaller particles of between 10 and 12 microns that get past the primary filter.

In instances when the engine is being subjected to severe service operations, a secondary filter of between three and five microns can be installed to filter even finer particles. For the filtration process to move smoothly, fuel pressure must be relatively high. A lift pump ensures pressure remains high even when fuel level is low in the tank.

The primary filter is normally situated between the fuel tank and the supply pump while the secondary filter is typically housed between the supply and injection pumps. This positioning ensures that all fuel from the tank has to go through the filtration process before it can get the injection pump. The design keeps the engine safe from impurities.

Types of Filters

There are different types of filters; some are referred to as the shell and element design. Filters of this design have an internal element that can be replaced, thus when the element runs, out the whole filter doesn’t need to be discarded. This filter element is normally located inside a shell, thus the name ‘shell and element.’

Many people don’t prefer the shell and filter design because it takes quite some time to change and therefore diesel fuel filters suppliers may not always have them in stock. They prefer the spin-on filter which takes much less time to replace.

In the case of spin-on, the entire filter is discarded and another screwed on. You should always check whether the filter is in good working order as part of your regular maintenance. If the filter turns dark brown, black or sticky and greasy, it is time to replace it. Sometimes diesel filter manufacturers specify the number of Kilometers after which the filter should be changed.


A typical diesel filtration system consists of the following parts

  • Gasket
  • Sealing washer
  • Base of filter
  • Seal ring
  • Pull rod
  • Bleed screw
  • Jump ring
  • Overflow valve
  • Filter element
  • Spring seat
  • Tray
  • Shell

Other Essential Parts of Its Operation

From the fuel tank, fuel is pumped into the filter by the fuel pump. The filter paper element, then removes impurities from it, allowing it to get into the fuel filter cavity. The filter is fitted with a return valve which allows fuel to return to the tank when the pressure is too high in the filter cavity.

More often than not the pressure gets quite high in modern engines due to the fact that a lift pump is now a standard part of the engine. Care should be taken when replacing it to avoid connecting it the wrong way

Paraffin Particulates

Besides cleaning other impurities, the fuel filter keeps the larger paraffin particulates from entering the engine and lowering its efficiency. There is a heater inside the filter that burns the paraffin melting it down to keep its waxy nature from clogging engine valves. The clearest indication that your engine could be clogged is when it stops working. It could also start to grind whenever the driver attempts to shift gears.

To keep the filter and lift pump from being destroyed, they need to be kept away from heat sources. This means that the best place for the filter to be located would be outside the engine compartment given that an internal combustion engine emits a lot of heat.

Leave a Reply