The diesel fuel filter is a very important part of the fuel system. This is even more true with the advances in diesel fuel system technology. With todays modern diesels with common rail, high pressure fuel pumps, fine tolerance injectors the fuel filters role becomes even more critical.
The main pic is of a Toyota Hiace D4D engines fuel filter. This filter was 30000km old and still inside its normal replacement period. This vehicle had consumed some dirty fuel and filter had done its job. Its easy to see the build up of particulate in the old filter when compared to a new filter (refer main pic).
The Toyota Hiace and hilux both have a sensor which will turn on a light on the dash when fuel flow is effected by a dirty filter, as do some other makes and models. When this light comes on a filter replacement needs to be carried out asap. Otherwise replacement at the predetermined intervals set out by the manufacturer should be the minimum.
Fuel filter replacement is a very cheap when compared to the problems that can occur by ignoring this task. The fuel system components (fuel injectors, Injector pump, High pressure pump etc) can be some of the most expensive individual items in a vehicle. And these items need to be running perfectly as not affect other items in the vehicle. (read as, very expensive engines, DPFs etc)
When your diesel is serviced next, ask your Certified Automotive Mechanic if your fuel filter requires replacing.