I haven't used one yet, but I just assumed that there were two flow meters, one incoming and one outgoing & the gauge or whatever calculated the difference. As far as I know all engines, diesel and gas, have both lines, to prevent vapor lock. I found one over at JC Whitney, but they don't have an installation diagram or anything.

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Michael Roth

1982 300TDT Wagon
1982 240D Euro!, 4spd manual-Parts car now, dead engine
88 Jeep Grand Wagoneer-fixing up for offroading
1989 Ford F150 (rust bucket) For Sale!
1953 Dodge B-4F, 1 1/2 ton Stake Bed (new restoration project)