Diesel Fuel Maintenance
Diesel Fuel Maintenance

What is fuel maintenance and why is it important?


Fuel polishing (or cleaning) is critical for modern day diesel engines. The tolerance for contaminated diesel fuel in these engines is considerably lower than in older eng​ines. Contaminated fuel can potentially cause engine failure. On-site fuel storage plans are vital to the reliability of backup power systems. When the fuel system fails, emergency generators are rendered inoperable. Fuel cleanliness is especially important on diesel engines as the fuel injectors and pumps clog easily when not maintained properly.


Long Term Storage

Diesel fuel will deteriorate if stored for more than a year. When high capacity tanks are used, fuel should be periodically drained and replaced with fresh fuel. If draining the tank is not possible, a fuel polishing system can be used to clean the fuel. The purpose of a fuel polishing system is to remove contamination such as water and dirt from diesel fuel to ensure adherence to fuel specifications and reliability for engines.


Catalyst and Exhaust After Treatment Devices

Most diesel engines manufactured after 2007 require the use of ULSD fuel. Diesel engines that have catalysts or other exhaust after-treatment devices, should only use ULSD in order to avoid poisoning the catalyst with sulfur.



Adding ULSD to a Tank with Existing Fuel

Each time new diesel fuel is added to a tank with existing fuel, the existing fuel “churns” which increases the risk of accelerating the oxidation process. Before adding fuel to a tank with existing fuel, check for water contamination in the existing fuel. If there is no water contamination, add biocide as a preventative measure, and then add the new fuel. When a high level of water is detected, best practice is to remove the old fuel and replace with new.


Maintenance and Treatments

“The quality of the diesel fuel in extended storage can be unpredictable due to the accumulation of contaminates resulting from oxidation.” EGSA: On-Site Power Generation, 5th Edition. At FM Generator, we check the condition of diesel fuel at every maintenance visit. Checking for water contamination is a must, as water collects due to normal condensation on the tank walls. If fuel tank levels are maintained near full, less condensation occurs as the tank’s free surface area is smaller. If the tank is kept water-free and treated with a biocide, the risk of microbiological contamination is minimal.

We highly recommend the use of biocides and stabilizers for diesel fuel as these prevent degradation of the fuel when stored for long periods of time. Stabilizers inhibit oxidation of the fuel. When diesel fuel oxidizes, it creates a sticky substance that can clog fuel filters and diesel engine injectors. Biocides and stabilizers are not effective, however, when fuel is already contaminated. These treatments are preventative measures and cannot be used as corrective measures.

If we discover contaminated fuel, we will recommend a fuel polishing service. Fuel polishing removes oxidation and sludge from the existing fuel in a fuel tank. The ULSD fuel commonly used today can hold twice as much water in suspension as Low Sulfur Diesel which requires better maintenance, especially for long term stored diesel fuel.

We also recommend regular fuel sample testing. This is done by taking a sample of the fuel and submitting to a laboratory for detailed testing. Consistent testing of fuel (and all generator fluids) can be extremely helpful in identifying issues before they cause catastrophic failure of the equipment. Regular testing can identify trends which can guide in proactive repairs.


Fuel sample testing and fueling services may be added to a maintenance agreement or fueling services can be done as needed. For more information, please contact us at 800-253-6617 or sales@fmgenerator.com. We can also be found online at www.fmgenerator.com.