Free: Contests & Raffles.
Some white jug Power Service diesel additive is good insurance for anti-gelling plus helps lubricate the fuel system. I use it year round (silver jug in warm months). As stated above fuel in cold climate areas is often a No. 1 & 2 blend to lover the wax/gel point of the fuel. Plugging in isn’t required on a lot of newer diesels but when below freezing it helps them start and warm up so much easier. I personally have mine on a timer to come on a couple hours before I take off in the morning. Plenty of time to get everything up to temp .
4-6 years is probably average here, I'd say.11 years is almost unheard of! You got your money's worth out of that one.
I always plug mine in if it's going to be below freezing if for nothing else than the heater warms up almost instantly I have an anti gel treatment I use when it gets below ten or so as most of my fill ups are in Seattle where winterized diesel is apparently as available as moon rocks.