I have a 1990 300SE with 180,00 miles. I drive about 90 miles a day. For rush hour driving on the highway I get 19.5-20.5 MPG. A nice open highway at 75mph without any slowing I get 22-23.5 mpg.
Hope that helps,
byt the way the car is a dog from a dead stop but on the highway it move right along
1969 RS/SS Camaro Conv. L-89 Alum. Head 396 375HP 4-spd
1987 GNX #419, 2002 RX300
FS: 1934 Ford Street Rod, Blown 383 $48,500 Firm