In the oil???

I would not. ATF is a lighter oil and does not provide the lubrication you need. It may actually clean some sludge in the oil system, But I would rather see you put in Synthetic oil, it will do the same thing. When I was 16 and worked at a gas station in New York the mechanic ther used to use ATF to clean his hands after work. If worked better thatn anything available at that time. If my hands are really bad, I'll do the same thing and use GoJo to take off the ATF.

In the fuel tank??

This use to be an old wives tail that has been passed down for quite some time now. Used to heer it back in 80 when I got my 220D. Mercedes did a test of the ATF in the diesel fuel idea. They found it actually caused the injectors to clog more than it helped. After the test Mercedes advised not to put ATF in the tank.

Mercedes does recommend Chevron Tectron as an additive to clean injectors. Techron and an Algea treatment are the nly additive Mercedes recommends.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car