This is some info on the temperature ranges when Diesel fuel gels in very low temps, how and what the effects are on diesel fuel.

Also included are some additive ideas to prevent this outside what the fuel refineries add, of interest, in the much older diesel engines, a blend of Kero and diesel was used to help prevent this from happening.

There are also commercial additives that are probably best suited to the more modern high tech diesel engines and their engine management systems and, much lower temps such as found in the winters of Alaska and Canada.

Like most fuels, diesel is a mix of hydrocarbons, and the components have different freezing points. For Number 2 diesel, as the ambient temperatures drop toward 0°C (32 F), it begins to cloud, due to the paraffin in the fuel solidifying. As the temperatures drop below 0°C, the molecules combine into solids, large enough to be stopped by the filter. This is known as the gel point, and generally occurs about -9.5 degrees C (15 degrees F ) below the cloud point.

This forum link also provides some info on Bio diesel and anti gel combinations including kerosine.