Another experiment...

I put my samples in the fridge. The samples were all dark brown, no visible sludge, at the time because the bottom layer had melted back into the oil.

I a short time the whole sample turned gravy.

I guess the rapid cooling caused the suspended fat to resolidify faster than it could "fall" to the bottom before the oil started to thicken & gell.

Probably the slower cooling at night allows the fats to solidify and fall to the bottom before the oil thickens up.

I bet the best thing for setteling is to place the barrel in a place that has minimal tempature variation. A cool, but not cold place. Without sunlight to prevent convection currenct inside the oil drum.

Once the oil has settled and been filtered, it probably doesn't matter much if it's stored where the temperature or sun varies as there is probably not much, if any, fats left in the oil anyway.

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1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5