[jws]

my diesel car had no big problems with -19°C

It depends on the formulation of your diesel. If you had a tank of "summer diesel" it would be gel at that temperature. Generally the supply chain starts changing the formulation as the weather gets colder and everything is good until you get to arctic temperatures. But if you fill up at a station that doesn't sell a lot of diesel and they still have summer diesel and its an early cold spell, or you are driving a vehicle you don't fill often, you can be in trouble. There are also additives you can add on your own if you know you have summer diesel.