I've seen the Stanadyne and Power Service get thick also when it is straight in the bottle. I believe that when mixed with diesel it lowers the pour point, kind of like gycol must mix with water before it offers freeze protection. I usually keep it in the garage until I plan on fuelling up then take the bottle with me to the pump.

Beware, when it was -40F I saw that the Gas Line still had #2 diesel in their tanks. They did post up this info, but I wonder how many people gelled their fuel tanks? I had some #2 left in my skidsteer loader and it wouldn't start. I added 5 gallons of #1 and some Stanadyne but this didn't solve the problem. I finally added PowerService 9-1-1 and was able to start it. It didn't run great, but good enough to pull it in the garage.