Is it normal for a 1984 300SD to rev at 3300 RPM at 70 MPH, i seen a 300D (turbocharged) about the same year that revs 3000 rpm at 70 MPH...

So is this normal to you????

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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

They both have the 3.07 rear end, so they should both be registering 3000rpms at 70 mph. Now, you may have an optimistic tachometer, which is not uncommon considering the age of your car.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

Both are okay. The MB tach isn't precision tool.