Welcome TireFriar to unique world of Diesel propulsion.
The interesting part of this thread, is the major variations in Diesel fuel around the country depending on season, and the origin of the refinery location where your fuel is sourced from.
Most region fuel pump brands adhere to the barest minumum, and only when there is either legislation or demand, do they change the formulas based on the ambient temperature.
Here' Why:
As the temperature gets colder the diesel fuel has a tendency to self-change from a liquid to a solid. This is termed "gelling". Its the process of the fuel changing state similar as "Jello" congeals together as it cools in a bowl in the fridge.
But the good thing is that it is reversable, and by letting everything warm back up again, the fuel returns to its normal flowing state.
VW built the engines for operation over a variety of temperatures, and the Diesel fuel companies compensate for the seasonal variation of ambient temperature by blending in more D1 diesel in the winter months (or Kerosene, it is the same stuff, just a different name).
But the great state of CAlifornia, is unique onto itself, and this is due to the formerly bad air quality that was prominent in major urban areas from the 70's on to today.
So, if you wish a Hotter burn to your ride, you add EHN, but only up to a level of 1200 ppb, and the downside of this additive, is it increases NOx levels.
The other part is to prevent gelling, in colder elevations when you transition for an evening up to the higher elevations, where the fuel was not treated, and you let the car sit then get cold after being shut off. It does not happen if the fuel is kept running in the engine if you are making a transit across the mountain passes in a 4 or 5 hour session.
But, if you are just in the lower elevations, there is no other additive needed, since the fuel available from your local Costco, probably has everything it needs , and then some for CAlifornia emissions, which are the toughest in the world, I am told.