Just picked up a 95 F-150 2wd 5spd with 164k. Haven't even done a tune up on it but with a combination of city/hwy it's getting 21mpg. I'm pretty impressed, we'll see how plugs/ wires etc improves that.
I'm running the stock '95 cam, and '95 dual EFI exhaust manifolds. I'm also running the ignition timing right on the ragged edge. I wouldnt be able to pull a trailer with it set like that, but I use the wife's '96 5.8L Bronc for that stuff anyway.
I consider 1000 miles the minimum for a truly accurate MPG calculation. That removes all variables due to weather, fill level, unusual traffic patterns, etc. I've been logging the Mazda6 since I bought it. Over 29K miles it has averaged 26.5 with a high of 35.7 and a low of 20.5. Single tanks prove nothing.
The tune up really helped throttle response but didn't seem to affect mpg. Still dancing around 20. Driving is a mix of back and forth to work and then driving out in the sage on wknds. Speedometer and odometer are accurate.
i believe it was the front driver's side brake assembly... the wear material on one of the pads was gone, rivets eating into the brake rotor, metal on metal contact, and i was so broke that i couldn't afford to replace everything
this didn't stop my supervisors from having me man the remote station, or me from visiting this cute little thing over in Waldorf... went through about three tanks total, i think the average was 21.6 or so, i noticed that the milage was excellent so i kept it up for a while
because those brakes were so bad as soon as i even saw a red light i'd start coasting, i'd let fully loaded semi-trucks accelerate faster than me, when i had to come to a stop i'd gear down before pressing the brakes, downhill in neutral, never went above 45 on a two lane, never went above 55 on a four lane, stayed off of the Beltway and I-95 completely
My 84 with 2.73 gear and 4 sp OD manual, 130k miles, with all the emissions stuff still attached and working, now gets 18-22 mpg over 2500 miles or so. With an even mix of city, rural and highway. The brand of gas I buy seems to have the greatest impact. Surprisingly the off brands get the better mileage, consistently over 20. I bought the truck new and never got better than 15-16 mpg from then until now. With the increase so far I wonder if 25 is possible.
You start to hit an aerodynamic wall after about 23 mpg, where you can't get much better fuel mileage because of the huge frontal area of the truck, as well as the mass you're trying to keep moving. The 300 in something like an old Datsun 280Z would probably be capable of 30 mpg, but the only way to get that high in a truck I believe is with a diesel.