A best practice for generator maintenance is to test the generator by running it once a month. Prior to start up, see if the fuel filter has a visual transparent bottom where you can see the fuel. If it looks like dirty fuel take notice, this could be bacterial growth. Run the generator to use up fuel and order regular top offs when it gets below 3/4th of a tank. After cycling the fuel, take a peek, make sure the fuel being pulled in is bright (not dark and degraded). If you are seeing any water (even a small drop) that is an indication of real concerns.
The fuel quality will usually stay within specification if you are using up half a tank a year and adding to it. If you have worries the easiest way is to just start over. With older generators, sometimes it’s a good idea to just evacuate the tank (empty all the older diesel fuel). Replace it with fresh diesel, treated and stabilized for long term storage.
Most back up generators are seeing routine annual maintenance where the mechanical needs of the equipment are walked through. If this is occurring, ask for a bottom sample from the back up generators fuel tank. Also, ask to see what the fuel in the bottom of the fuel filter looks like(assuming they are changing that). This would give an indication if problems might exist deep in the fuel tank.
Give us a call for more support and a free fuel sample to ensure your fuel is high quality.