I have a '91 300-SEL with about 95,000 miles. If I drive a consistent 70mph and am not dealing with a head wind, I can get as much as 22mpg, but 20 is more the avg.
Keith mentioned what I would think to be good mileage for a 4.2l V-8. I've read other comments here that mirror Keith's. I wouldn't rule out the 420SEL.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.