360ci

Keep in mind that the EPA tested pre 07 vehicles at a highway speed of 55mph. I had an '08 Escape Fwd as a loaner when my Taurus was in the shop for a few days and I calculated it out to 22mpg mostly highway at 60mph. At that speed the engine was turning over around 2000rpm. OD off has its way with fuel economy depending on weather, road and driving style. OD off is best when towing or carrying heavy loads through town or on hilly terrain. This keeps your transmission from constantly shifting and keeps temperatures in check! Your foot and mind (aggressive driving) is the biggest factor in fuel economy. If you are not on flat roads cruise control can even hurt your mileage (ever so slightly). If you coast a bit going up hills and lose some speed (2-3mph) you'll save 1mpg right there.

There is no 'valve in the engine' that opens up to allow more fuel into the engine. Fuel injected engines put as much fuel into the engine as you press the go pedal farther into the floor. Once you get into OD gear (30-35mph or so) you can double your rpm from that point to get optimal highway mileage and the engine isn't going to lug or downshift when you go up hills.

Keep the fuel economy up with a properly tuned engine and properly inflated tires. Coast to red/amber lights and going down hills, stay within 5mph of the speed limit and you will see an improvement!

Not to brag, but my (dodge) AWD 5.9L V8 gets 18.3mpg at 55mph.

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'99 Taurus 3.0L 2V Vulcan 145hp; 107,820m
'00 Durango R/T 360ci 300hp (modded); 90,651m
'06 Pontiac G6 GT 3.5L 220hp; 14,224m

Amsoil in all vehicles!