Thanks for the responses, gentlemen. I have calculated that I have 170.3 (1/4 cups) capacity in the fuel tank, which means that the ratio of fuel/additive to "car wash" is 169.3:1 which seems like a small amount to me. Gladly awaiting any other comments though

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Nello Tare

1982 300D (266,001 mi.) looking and running great

Previously owned:
1976 450 SLC
1983 300D
1976 300D
also
1982 Jaguar XJ6 (loved, but gone)