Aha!!, A clue, and a good one.
Just when it starts to get cold, huh? Well, Here is my conjecture. Just as the weather starts to turn colder, either you, from what remains in your own storage, or your fuel supplier from his storage tanks, or even his supplier, is still pumping down the last of the "summer" fuel, blended for summer temperatures when things like pour point, wax content, etc., aren't critical. Obviously, these things matter in winter, not only to a trucker in Minnesota, but to an air plane pilot sitting on the tarmac in Minnesota.
Could be that he is actually delivering winter fuel, but you have enough residual summer fuel in your tanks to "blend" his winter fuel back up to closer to a summer blend.
Maybe he is still "blending up" to winter conditions, and your residual summer fuel is "blending down" the mixture, bringing the total fuel more close to a summer blend for a short period of time.
So, as It turns colder, this quasi-summer fuel gels up, maybe a little, maybe a lot, and plugs your filters impeding the flow. Can you get fuel filter differential pressure data from the time frame in question??
And then, by the time you think this thing is eating your lunch, you get some fuel turnover via a new delivery that either replaces or dilutes your quasi-summer fuel, and the problem goes away, and everybody forgets about it until next fall, when it all happens again.
Believe you me, I became a believer one December 6th in Louisiana, when it was 6 F outside, rare for LA, and when a neighbor (older widow woman) asked me to bring my big old powerful diesel pickup truck down to her house to jump off her poor little Mercedes diesel. (It did not have fuel problems, just a dead battery. ran like a top when I jumped it, after grazing a fire plug by her driveway while distracted by fuel tank switching described below)
Problem was I don't use the pickup truck regularily, so it was sitting there with summer fuel, and not plugged up. The fuel filters plugged solid immediately. It is the only time I have ever seen the warning light activated by high differential pressure across the fuel filter, ever. The engine ran terribly, if you can call what it did running at all.
I quickly threw a heavy dose of fuel treatment, which contained pour point depressants among other things, into the almost empty tank, and, I swear I could tell when that treated fuel hit the filter/engine. It smoothed out, and purred like the kitten that it is. Since this tank was almost empty, and I live in a hilly area, and was concerned about the fuel pickup in the empty tank sucking air, and losing prime, as it had before at low fuel levels in that particular tank, so I had to keep switching back and forth between the empty tank, with its load of heavily treated summer fuel, which the engine would run on, and the full tank, which had summer fuel also, but with no treatment, which made the engine run terrible.
I had to nurse this combination of treated/untreated summer fuel to a service station several miles away, after jumping her off, where I knew their fuel was obtained from a local refinery in the area, and would be seasonally adjusted for the current winter conditions.
I told that anecdote to say that fuel gelling is real, and fuel seasonal blending is real. And, the wrong fuel for the season can wreak havoc.
Isn't the prist you mentioned just a water problem solver?? Isn't it an alcohol that serves as a water transporter, and an antifreeze for the water that might be in the fuel???? I thought I remembered your saying that is all you use. You might want to look into an additive that would give you a pour point depressant, and a wax problem solver. At least for the period when you suspect that this might be a problem.
Other than that, I have no idea what might be your problem.
Keep us posted.
rmw
