The fuel tank is vertical with the top of the tank near the filler neck. If you have a loose fuel cap it will spill out on right turns if the tank is full.

You can shift from 5th to 4th by just pulling the shift lever toward the drivers side, if you are left hand drive. If you hear an rpm change you were in 5th. Your winter/summer switch should be in S so it will start out in first gear. Then you should be able to count the shifts.

I have the naturally asperated version of your car. The rpm figures you mentioned sound normal for my car, but the rear end on your turbo might be different. Mine runs at about 2700 at 70 mph in 5th.

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'97 E 300 D