Diesel Engines, Hard to start and Lack of power

These are indicators of inadequate fuel passing through the engine, thus not providing the necessary fuel to complete the combustion process.

This may mean that the fuel system is partly blocked. The fuel filter, located in the fuel supply line between the fuel tank and the pump, is most likely the key problem.

The fuel filter is element that containing a special paper cartridge (think of a toilet roll in a container with an in and out port) The filter extracts particles and some of them often extract water that needs to be emptied at regular intervals from a small tap.

Points to note

Clear and light means the fuel does not contain any visible drops of water or other particles and without haziness or cloudiness. Sometimes the filter bowl has some contamination, this is natural and generally does not cause filter blockages, except it was in large quantities.

Common Diesel Fuel Problems PDF Downloads

Some of the common causes of filter blockages

Suspended Water

Suspended water can be seen a fuel haziness that is considered a problem for engine operating correctly. This issue can be overcome by ensuring that settled water is drained often from the tank or filter drains if applicable.

Suspended particulate matter

Dirt, rust, or oxidized fuel, may form a suspension of particles, creating deposits on the filter elements. Filter and fuel laboratory analyses will be needed to ascertain the causes. Issue resolution can include fuel cleaning and/or better management of fuel storage systems.


Wax looks like a bright yellow suspension in the fuel during cold conditions. If the fuel is cooled below the allowable operating temperature, it will create a yellow solution that can block filters.

This happens due to the use of the wrong fuel for the season or area, for example, if you use summer grade ADF in the winter season or bring ADF from warmer areas in the winter to a colder region.

Fungus, algae and bacteria

Fungal pollution is a result of wrong or poor drainage of water. It is usually related to free water, hazy fuel, suspended water for a long time.

You can detect them as a black or dark chocolate slime that will block the filters. Fuel laboratory tests are needed to confirm that fungal growth in your tank exists.

For rectifying these issues, you will need to change filters, drain all storage tanks of water and sediment. Severe pollution may need a thorough cleaning and polishing of the tank and biocide treatment.

Normally problem happens mostly in the warmer seasons as bugs love higher temperatures to reproduce.

Diesel fuel testing

The easiest way to check for the above issues is to take a sample of the fuel from the tank and use one of our high performance test kits.

If the fuel is clean and bright your fuel is probably ok to use. If the fuel is hazy or has some particles floating in it, you should check it further for problems.


Often customers treat their fuels with additives, which can block filters if they are added or mixed into the fuel incorrectly.

Additives will not remove slime; in fact, additives will loosen up the slime causing filter blockages in some cases.