300' for testing. You need to know what the failing point is going to be.

Day to day driving is about 200' but the coolant can reach about 250' in extreme situations.

I need to know that 250' is safe and not on the edge of failing. If the stuff will hold up to 300' then I am safe at 250'

You gotta plan for worst case senario.

Normal fuel line will not efficiently transfer heat from the coolant to the WVO.

__________________
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