I have started old tractors and trucks that had some 8-10 year old diesel fuel in their tank. Fuel gelling is usually a condition of cold weather. Most diesel selling places put some additives into their fuel when the temps go down. You cannot have too much anti gel additive when it is cold, just costs a bit more.
Near water, diesel fuel can pick up a bug that lives in diesel and is a kind of algee. I think the only way to get rid of this bug is to have some company come and refilter all the fuel. This is a big deal on boats.
Diesel engine injection pumps will not pump air or self prime themselves. If there is a good supply of fuel to the fuel pump, it will make about 8-12,000 psi
at the injectors. The most common reason for a need to reprime an fuel pump, is the supply fuel line gets a rusty hole of the fuel line rots and allows air into the fuel system. Never add gasoline to the diesel fuel for many reasons besides my health.
If ya grind down a couple batteries trying to start an engine, consider the fate of the starter. When battery voltage becomes lower, the amperage skyrockets.
Low batteries kill starters. Frank In Idaho