I would not keep a diesel tank low on fuel, there are nasty bacteria that thrive in the wet, dark and hot fuel/water mixture. Once that bacteria has past your fuel filter is game over for the engine ! The byproducts of the bacteria are so acid that it disolves the fuel lines and seizes the injectors/pumps when it occurs.
Thread Drift Warning!!
I believe you are on about
cladosporium resinae (sp?) which is a ****** if you get it.
It does live in diesel, but prefers Kerosene if given a choice.
It isn't very common in the UK, due to the cold weather. If you keep the tank low on fuel, you get condensation. 'Gladys' lives on the fuel/water boundary so condensation will encourage growth. You will first notice a brown slime in the fuel filter if you have it. The excretion products won't cause any problem in a plastic tank - but as Chris says, it is acidic. Your lines and injectors
should be safe if you run the car every few days. There are products to kill it off, and to prevent reoccurrence. I have a stock of
Biobar (for my heating kero) that I 'found'. The problem with the shock treatment is when it dies, it then goes through your system and clogs everything. It is easy to wash the slime out though.
âBack on topic
As everybody says, brim it, zero odometer, drive it, note milage, brim it, work it out.
This is the only way to check your MPG properly. We use the app 'road trip' for our cars religiously and it is a good indication of the health of the car.