I recently purchased a '97 E300D with a 4 speed automatic transmission plus an overdrive gear. Should I keep the car in 4th gear all the time or always use the overdrive? I've heard some people say not to use the overdrive gear because the engine rpm's are so low and that will cause problems such as carbon build up. I asked someone at the dealership and he looked at me like I was crazy (said use the overdrive) but I got the feeling he didn't know what he was talking about. Usually, I always have it in 4th unless I'm on the interstate; then I'll use the overdrive as long as I'm going fast enough to keep the rpm's at 3k or more. Does anyone have thoughts on this?

Scott

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Scott
1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)