Antigel or depressant?
To make summer diesel fuel suitable for the cold season, it is necessary to find effective ways to influence paraffin crystals, which form in the fuel with temperature drop. The so-called pour point depressants partially handle that problem: without influencing the total amount of paraffins in the diesel, the depressants modify and soften the precipitating crystals, which allows the fuel to maintain adequate fluidity even at lower temperatures and to pass through fine filters unobstructed. However, no depressant can save winter diesel fuel from precipitation of paraffinic hydrocarbons, the result of which is fuel separation when stored in cold temperatures into two layers: the upper clear layer and the lower cloudy layer.
If the separation occurs in the fuel tank, the engine will most likely start, but will not work for any long time: the crystal phase of the fuel will quickly clog filters, which will cause the engine to seize up or fail under any load. Summer diesel fuel diluted with gasoline is especially prone to separation in cold temperatures, although back in the day this way of making winter diesel fuel was quite acceptable.
The correlation is simple: the more gasoline there is in the fuel, the higher the probability of separation. Besides, diluted diesel is inferior in terms of lubrication, which will definitely take its toll on the longevity of the fuel systems. To prevent separation of diesel, chemists came up with anti-gel additives. These compounds convert paraffin into suspended state, which makes fuel consistency uniform throughout the volume and prevents sedimentation.