Frank, I have not done this but was told by the service rep at the local Mercedes dealership to use ATF with every tankfull of fuel. Also have heard of filling the fuel filter with ATF when you change filters, this is a convenience for not having to get diesel fuel to fill the new filter. The service rep told me that using ATF will smooth out a rough idle. I do not have any proof of this.

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Richard Seaman
1982 300D Turbo 198k
1987 420SEL Sold
1993 400SEL 123k
MBCA Desert Stars