crumm did a test- different mason jars with fuels and additives. it was interesting.
iirc, it will start to cloud, form wax crystals, more cloud as it gets colder until full gel. bio is worse than d2. i want to say 10-15 degrees F. -10C for sure.
I left a bottle in my truck and at -10 deg F, it turned really cloudy. I use a half of a bottle per tank with no problems. I do not use bio-diesel. I heard some 18 wheelers cussing it at the truck stop.
Here in the north of Canada I can start my truck at -40C or F with no additives. The supplier adds additives as required to allow free flow of the diesel fuel. Called winter grade.