Short answer
Stored diesel can collect water, sediment, and microbial growth, and it can degrade over time. Drain water, sample the fuel on a schedule, treat it as the results indicate, and keep records alongside generator test logs.
What goes wrong in stored fuel
Condensation adds water, which supports microbial growth at the fuel-water interface. Sediment and degraded fuel can clog filters exactly when the generator needs to run.
Ultra-low sulfur diesel and biodiesel blends can be more sensitive to storage conditions; follow your fuel supplier’s guidance.
Test on a schedule
Sample from the tank bottom, where water and sediment collect. Test for water, sediment, and microbial growth, and for fuel properties if the fuel has been stored a long time. Diesel fuel is specified under ASTM D975.
Treat and maintain
Remove water, replace fuel filters, and consider fuel polishing for large tanks. Additives can help with stability and cold flow; use them as directed and as your fuel supplier recommends.
Keep records
Log fuel deliveries, test results, treatments, and filter changes. Records support your emergency power testing program.
Frequently asked questions
How long can diesel be stored for a generator?
It depends on fuel quality, storage conditions, and maintenance. Test periodically rather than relying on a fixed shelf life.
What is diesel bug?
A common name for microbial growth in fuel tanks, which feeds at the fuel-water interface and can clog filters.
Does stored diesel need additives?
Additives can help with stability and cold flow. Use them according to test results and your fuel supplier’s guidance.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].
