It has to get very cold for diesel to gel. I work in a hydrocracker unit and we make diesel and jet. The target freeze of the diesel in the summer is +20F, but in the winter the target can be as low as -54F, which should keep it from gelling up. But some are correct here, some companies have the distributer add anti gelling additives to their diesel before it is delivered to their stations. Also even the southern diesel freeze target is just as low as ours because a semi can fill up in a southern state and arrive in a very cold state on that same tank of diesel. We start making winter diesel early in the fall to make sure it is available when the cold weather hits. I have driven in -25 F without any issues. I am 64 and been driving and operating diesel equipment all my life and the only time I had diesel gel was at -48F. But I do add a dose of Stanadyne, but not so much for anti gelling, but for the lubrication qualities, especially with the ultra low sulfur diesel today.