It's actually wax. Diesel contains a lot of paraffin, and at a certain temperature (called the "cloud point") the wax begins to form visible threads and the fuel gets cloudy in appearance. Problem with waxing (or gelling) is that the fibers of wax begin to pile up, especially on the fuel filter, and block fuel flow to the engine injection system. You'll first notice it as a rough idle or loss of power with engine stutter - then it will stop and not want to refire. There are "shock" additives, but it's much harder to recover after the fact than to prevent up front. Emergency treatment can be dosing the fuel tank with kerosene or an anti-gel and swapping out the waxed-up fuel filter. A severe case can often only be resolved by heating the fuel and fuel system (whole truck, actually) back up well above the cloud point in a warm garage (it takes more heat to get the wax to dissolve than the temperature it takes for it to form). Waxing/gelling has been a problem this winter with the swap to Ultra Low Sulfur Diesel (ULSD) fuel because ULSD has a higher cloud point than low sulfur diesel. The distributors are supposed to be additizing the fuel for lubricity and "winterizing" it for your location, but many of us are taking no chances and adding our own treatment for anti-gel and lubrication.
You can ask your station where you fill if they allready blend the fuel at all. Where I fill up, the station blends 70/30 all winter. Haven't had a problem yet. -11 degrees F this morning and no problems. Allways a good insurance to use some additives though.
I've been thru some nasty Wisconsin winters, but this one has been hell. The USLD has gelled me and took 24 hours in a 55 degree shop to get out. That was after changing filters (factory and nictane), adding 1 qt of PS white - then 1` qt PS 911 - then 12 oz of Howes. It gelled to almost solid at only -15F. I had a normal dose of PS white in the tank to start with.
I've driven with no issues and no additives down to -25 and -30f. This hasn't been just me. The local waste hauler bought up one stores entire supply of anti-gel and rescue stuff. (day before I got there...) I blame the distributors for not dosing correctly.
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