Agreed.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"

I'd plumb the return loop after the filter. This would effectively add heat by reducing the amount of cold veg fuel drawn through. Before going on another winter trip with 10 below weather, I'd also add electric heat around the filter with a switch in the cabin.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"