I have about 40 gallons of year old diesel fuel that has been stored in a pickup bed steel fuel tank. I use a water removing fuel filter on the pump and have anti-gel conditioned the fuel when I filled the tank. Can I safely mix this fuel with current purchases say 5 gal per 30 gal fill to use it up or should I just dump it. At $2. 39 a gal I am not happy about dumping it. I had been using the fuel for a diesel mower I have but it broke down and I haven't used the fuel.