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Parker Engine Mobile OE: Racor Products Blog & Information - North America

Cold Weather Diesel Fuel Filtration

Cold Weather and Diesel Fuel:

After an unusually cold storm you may wonder why your diesel vehicle had low power, or wouldn’t start in the first place. What with gasoline vehicles driving around without a care, why is it diesel vehicle owners have so many cold weather problems? While filtering diesel fuel is always necessary, filtering diesel in sub-freezing conditions often leads to plugged fuel filters and poor engine performance. It all comes down to diesel “cloud point” and “pour point”.

Cloud Point:

All #2 diesels contain naturally occurring dissolved paraffin waxes, which contribute much of the power density diesel fuel is known for. Depending upon the quality and blend of the diesel fuel, its “cloud point” (the point at which paraffin crystals precipitate out of solution) may be 0°F to 45°F (-17°C to 7.2°C), or even higher.

Once these paraffin crystals drop out of solution, they quickly coat and clog fuel filter elements, slowing or stopping fuel flow and proper vehicle operation. In addition, any water present may crystalize as icy slush, slowing fuel flow even more quickly. Unfortunately, a filter clogged with wax and water won’t start flowing again until the filter and fuel is much warmer than the temperature that started the clogging in the first place.

In winter months and cold climates, fuel refiners blend #2 diesel with #1 diesel to fight cold weather filter clogging. The reason for this is that #1 diesel does not contain paraffin waxes; blending with #2 dilutes the amount of dissolved wax to the point that it no longer poses a problem. However, there is no guarantee the diesel fuel you get is actually blended to work at a temperature experienced by your diesel vehicle.

Pour Point:

Another (less likely) consideration for diesel fuel in cold weather is the pour point. Pour point is literally the point that the diesel fuel will no longer pour (flow freely) because so much wax has crystalized. If properly blended, diesel fuel will flow freely down to -20°F. The possible flow temperature drops to -40°F if using 100% #1 diesel. If your fuel goes below these temperatures, the result is diesel fuel with the consistency of a frozen drink.


The use of biodiesel by itself or as a blend presents yet another cold weather problem, as biodiesel holds much more dissolved water and has a higher cloud and pour point compared to regular diesel. Having a tank full of diesel fuel blended for warmer temperatures is a sure way to have problems on an extra cold day. So, filter clogging problems associated with cold weather are not a filter element failure; it is a problem inherent to using diesel fuel.

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