I have had a 1982 240D with a manual for 18 months. It needed work:new chain with spot on cam timing ,valve adjustment stock bosch injectors synthetic dif and gear box lube and synthetic oil. It burns 0 oil and doesn't smoke at all. It averages 32 to 33 mpg and on a recent trip to Montana I got 34.7 up and a mind numbing 36.7 coming back. I drove 55 to 60 and I had no wind issues. I carried no weight. I have verified the odometer which reads 2 % low so I made that correction. I have 195 14 tires inflated to 36 lb. My 1977 240 D manual Tranny got 32 mpg on slow trips and 29 mpg at 75 mph. I didn't believe the mid 30's but it's real and I also verified the numbers on the gps. I get 32-32 in going to and in town(mostly hwy). My 4 cyl camry does low to mid 30's at 55 mph as well which is the expected mileage. My 300D 1985 turbo got 25.5 to 26.5 at 55 to 60 mph and with new bosio injectors the last trip was 29.1 up and 28.9 coming back which is a pretty decent improvement. It has 300K miles but I have reworked the engine to factory spec as well with a new timing chain, valve adjustment, injector purges, alda cleaning etc. Slow driving helps the mileage. My cummins diesels(1994 and 1997) with automatics get 17 to 18 mpg at 70 to 75mph but at 55 get 21 to 22 mpg.