Diesel Fuel Filters: 4 Common Causes Of Plugging

Diesel fuel filter parts are expected to last an average of a thousand hours or more; however, their life expectancy can decrease significantly if they become plugged. Most consumers are under the misconception the plugging is caused by dirt; however, you’d actually need a significant amount of dirt for the plugging happen. Diesel fuel filters are more likely to plug up during the winter, as the temperatures drop. This article will take a look at the 4 most common causes.

Waxing or Gelling of the Diesel Fuel

The consistency and viscosity of diesel fuel change easily based on the temperature the fuel is in because the paraffin in the fuel crystallizes. Waxing of the diesel fuel happens when the temperature causes the paraffin to reach its cloud point, which is when the paraffin begins to form cloudy wax crystals that plug up the filter. The cloud point ranges from -18 to 20 degrees Fahrenheit.

The pour point on the other hand is when the paraffin crystals form a gel. This is also the lowest temperature at which the diesel fuel will flow. The pour point typically occurs anywhere from 10 to 20 degrees Fahrenheit below the cloud point. Make sure you operate the diesel-run vehicles in optimal temperatures.

Frozen Water Mixed into the Fuel

If you do not have proper fuel water separators installed with the diesel fuel filters, the fuel might mix with water. Water has a higher freezing temperature than the diesel fuel. If the water freezes, ice crystals will form and seal off the filters causing them to plug prematurely.

To prevent this from happening, purchase diesel fuel from a reputable seller to ensure water is not mixed in, as a higher water concentration is typically found in lower quality fuel. In addition, purchase a fuel separator that will remove any water produced through condensation.

Bacterial or Fungal Contamination

Subsequently, low quality diesel fuel will also be more likely to contain bacteria or fungi. These bacteria and fungi will grow quickly if there is a lot of water present. Large colonies not only plug up the filters, but will also produce acid that attacks other parts of the vehicle as well by causing severe corrosion.

If the cause of the plug is due to a fungal or bacterial contamination, you can purchase and add biocides to the fuel. The biocide will kill the fungi and bacteria; however, the acid that was produced will still circulate and will need to be removed with professional help.

Asphaltenes Caused by Mixed Fuel

Last but not least, diesel fuel filters can plug up if you have used different types of fuel or if the diesel has decomposed into asphaltenes after it has been sitting idle for too long. Asphaltenes look like black sludge and is difficult to remove. If the plug is due to asphaltenes, most experts recommend you replace the entire filter. You will need to remove the fuel in your tank and refill it to prevent this situation from happening again.


Regularly inspecting the diesel fuel filters will give you a good idea of the condition that it is in. The diesel fuel filters play an important role in the overall function of the vehicle and can make a huge difference to the overall performance. Do keep in mind that a plugged filter normally indicates that numerous other problems have been averted, as the filters have effectively done their job. There are many factors that cause diesel fuel filters to plug. It is important to spend some time uncovering the cause, so an effective solution can be recommended.