Fuel Filter Plugging – Microbial Growth and Issues

What’s happening?

In Spring, we need to be aware of substantial temperature swings that could increase moisture-related issues in fuel tanks. Tank maintenance programs using a combination of fuel cleaning, tank maintenance, and biocide products are instrumental in solving moisture-related issues (caused by microbial growth) and preventing the recurrence of future problems.

When temperatures change, warm air loses its ability to hold as much water vapor. This results in condensation and causes water accumulation. Freezing and thawing temperatures also lead to water in storage tanks (i.e. water can seep into cracks and crevices and expand as it freezes, leading to openings that can let water in). As end-users get moving this Spring, they should pay extra attention to moisture levels in tanks. When care is needed, additional levels of moisture control will help to suspend and remove moisture.

It is good to have a plan in place to deal with potential moisture-related issues and prevent future occurrences.

What is microbial growth? How can it be mediated?

Microbial growth in fuel

Microbial growth (commonly referred to as bugs or algae) goes hand in hand with high moisture levels. When conditions are right for growth to occur, these microorganisms thrive and can cause a wide range of issues in fuel storage tanks and vehicles.

These organisms use fuel as a food source, but they also need water to become active. As water saturates out of fuel and settles to the bottom, it turns into a breeding ground for microbial growth to flourish.

Proper treatment with biocides and tank cleaning chemicals can help ensure that customers’ tanks are clear of bacteria-related issues.

Read more here about microbial contamination.

Tell-Tale Signs of Fuel Filter Plugging

plugged fuel filter

A common indicator for microbial issues is a slowed fuel flow caused by filter plugging.

Clogged filters often become coated with and contain dark slimy substances in the filter media.

Many microbial growth forms also cause damaging corrosion causing a host of other problems. By far, the most common shared element between all types of microbial growth is the presence of a water bottom in the tank where the growth is occurring.

No matter how it appears, microbial growth can be very frustrating to end-users.

Tank Maintenance Programs

Tank maintenance programs are great for keeping microbial growth at bay and ensuring that fuel storage tanks are in good shape.

Typical tank maintenance programs include fuel cleaning additives. These additives can help maintain tank cleanliness and housekeeping operations ensuring that tanks do not allow in water and moisture. A tank maintenance program can also offer fuel testing to better understand your fuel.

Recommendations for Controlling Microbial Growth

Checklist for End-Users

Checklist for Drivers

Tank Maintenance Programs

Benefits of Tank Maintenance

Tank maintenance programs are not a new concept, but the need for tank maintenance programs is evolving and more important. Modern fuels are susceptible to a wide array of issues in storage, so taking steps to ensure that fuels are kept fresh and in good condition is extremely important. Moisture contamination is a constant threat that can result in operational shutdowns if not recognized and dealt with early on.

microbial growth in tank

When bringing vehicles into a service department for possible mechanical failure, mechanics often initially blame fuel for the issues. Having a history of monthly fuel quality analysis is a great way to help dispel guilt and get on the faster track of finding the cause of the issue at hand.

The benefits experienced by a tank maintenance program are wide-reaching. They can go a long way in securing existing business and attracting new business because of the additional advantage you provide customers.

Moisture and Tank Maintenance

tank component separation

The prevention of moisture accumulation is one of the most important aspects of tank maintenance programs. Customers with fuel storage usually depend on their fuel to work properly when called upon, but they do not take the time to inspect their tanks regularly. Taking a few minutes every month to make sure that there are no leaks, cracks, or other failures can go a long way in preventing future fuel issues. Click here for our checklist.

Water enters the fuel supply chain in multiple ways, including condensation, contamination during transport, leaks, and careless handling. The routine removal of this moisture prevents water accumulation and helps prevent ice formation, bacterial and fungal growth (“bugs”), oxidation, and corrosion.

All fuels contain a volume of dissolved moisture that is removed with fuel as it is burned during combustion. ET’s Moisture Control technology attaches to moisture and allows it to be burned off in the engine as regular dissolved moisture. This process prevents the formation of tank water bottoms that can lead to a variety of issues.

Basic Tank Maintenance Tips

Storage Tanks
· Use a tank maintenance additive that will prevent the accumulation of moisture and disperse and remove contaminants
· Pump out or drain moisture and contaminants at least semi‐annually.
· Use desiccant vent breathers to remove water vapor from the air as it enters tanks
· Understand whether tanks are level to identify where water bottoms will accumulate
· Double-check fill caps and venting for leaking.
· Inspect tanks for cracks, holes, leaks, or loose fittings and caps
· Keep snow and water away from fill areas
· Sample and test fuel annually
· Use an effective biocide treatment semi-annually
· Glycol ethers (moisture control agent) act as a co‐solvent for water and can help reduce water accumulation and enhance fuel’s ability to hold water in the solution and can help remove moisture from the entire system

ET Products can help determine the proper intervals to treat with an effective biocide to mitigate microbial growth before it multiplies

Vehicle Equipment Tanks
· As you enter the cold / winter season, change your fuel filter with a new clean filter of
appropriate size
· Drain off all water from water separators daily
· Make sure fuel caps fit tightly and do not leak
· Minimize condensation by topping off tanks at the end of runs.

Winter Preparation Suggestions for Diesel Fuel


If it is going to be very cold (click link here for minimum temperature forecasts), customers should make extra preparations to ensure that they have more success in operating equipment.  These include:

  1. Agitating tanks before use
  2. Allowing vehicles to warm up for longer than normal
  3. Moving portable fuel tanks indoors out of elements
  4. Starting vehicles during weekends to prevent settling
  5. SOS or like product on hand


Make sure your dispensing units contain fuel filters. Before freezing temperatures replace filters with larger micro filters typically 30 microns or greater. The filter should not be a water removal (hydrosorb) filter in most situations.

Make sure filters on diesel vehicles are replaced within regular truck maintenance schedules. If the truck or tractor filter is doing its job, it will contain some level of moisture. Typical cold start related issues are the result of diesel engine filters icing not gelling.


-Inspect tanks for areas that need to be shored up (vent caps, fill caps)

-Replace filters with at least 30 microns, and make sure that they are not old and full of obstructions

-Check for water bottoms and remove if present

-Treat the entire volume of the tank, not just the delivered fuel

-Check to make sure that the tank is located in a place that will not be leaked on from directly above if possible

Remind customers not to leave the hose in the snow!

How to prevent a plugged fuel filter with diesel fuel additives

Winter diesel fuel additives are used to prevent a plugged fuel filters and increase the winter operability of diesel fuel.

How can you prevent a plugged fuel filter?

When properly used, cold filter plugging point (CFPP) additives change the shape and size of wax crystals so they can pass through fuel system filters at lower ambient temperatures than without the use of these additives.

A wax anti-settling additive (WASA) can prevent wax settling if used in the additive package. WASA additives disperse the treated wax so it stays suspended in the fuel and does not settle on the bottom of the tank. The CFPP temperature is now more reliable due to the WASA component.

A caveat of diesel fuel additives and CFPP treatment: TIME

The longer a treated fuel sits in a “Slow Moving Tank” at low temperatures, the more likely gravity will promote the settling of wax at the bottom of the tank. 

The increased wax density overwhelms filters on startup (the fuel pick-up is normally on the bottom of the tank). Fuel filter plugging will occur at a temperature higher than the CFPP temperature.

Testing Methods Fuel Testing is of extreme importance. To evaluate wax settling performance in CFPP additives, a treated and untreated fuel sample is cooled to sub-zero temperatures. The sample sits undisturbed and time lapse photos are taken. 
The resulting photos show the rate at which wax settles and visually indicates the reliability of the given additive at a selected treat rate.

Conclusion It is notable that the additives tested exhibit significant differences in WASA performance. CFPP additives with higher levels of WASA additive visibly indicate the most reliable operability. 

When concerned about a critical application, i.e. such as a state DOT bid or another requirement that has a hard CFPP target to meet and penalties associated with non-attainment of the target CFPP, one should look for the additive products that provide the best protection from settling.

Preventing Plugged Fuel Filters with Winter Diesel Fuel Additives

Two fuel samples of the same fuel; all held at -15F for three days.

·Sample I: treated with CFPP additive at manufacturer’s recommended dose of 1000 ppm

·Sample II: treated with CFPP additive at manufacturer’s recommended dose of 800 ppm

Both additives claim to have a WASA component.

Sample I

CFPP additive @ 1000 ppm, reported CFPP = -28F Soak temperature -15F

Day 1: Settling Started

Day 2: Settling Intensified

Day 3, Settling is greatest, a vehicle no-start, wax will accumulate at the bottom of the tank and overwhelm/plug a filter.

Sample II

CFPP additive @ 800 ppm, reported CFPP = -30F Soak temperature -15F

Day 1: Homogenous Wax suspension


Day 2: Homogenous Wax, even suspension

Day 3: Homogenous Wax, even suspension