So ur running 80% diesel and 20% used fluids? I would definitely install a water seperator filter, in the line before the fuel even gets to the promary filter. the primary is the spin on right? or is it the littel clear one? Just curious. what would happen if u say raised the ratio to something like 50% diesel and 50% used fluids? will it hurt the engine any or what? BTW I live in southern california so it rarely gets below freezing here.