My '89 F250 4x4 4.9L (300 I6) 5spd. 3.55 235/85R16 70,000 miles etc. gets about 14 highway, 12 city, 10 towing. How does this sound? I just diagnosed a stuck open thermostat, but have not had a chance to test the mileage. I keep hearing people brag about their 300's gettin' 20+ MPG. Should I pull the side cover and check that the valves are all moving? Should I do a compresson test? I'm not that disapointed with the mileage but I'd appreciate more. I am not impressed with the power, I'm not a hot roder but, I can't even chirp the tires in 2nd gear! I once had an F150 spinning wet tires in 4th! What do you think?
Tyler

 

i get 14 or 15 out of my F150 so i say your close to being right some dude i talked to had a 2 wheeldrive I6 with 5 speed andn 273 gears he just got 15-16 miles gallon on highway