It seems when I drive my SuperCrew at 55 with no overdrive on and hitting 2k +/-, and driving it at 70 with overdrive on and hitting 2k +/- I getting better gas mileage at 55. Now, both speeds hit the same RPM. I can only think that where we live we have lots of hills and valeys, in O/D, she is always kicking out of O/D. Is it because it kicks out a lot, while not in O/D she doesn't hardly do it. Have the small V8.

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2001 F150 SuperCrew II Lariat 4x4-4.6 V8-508A Lariat package-Dark Highland Green-Leather Captains Chairs-P/U Bed Extender-Rear Sliding Window-Skid plates package-Cab.Steps-Lower twotone paint-Power drivers seat/autolamp-Engine block heater-17" Chrome Wheels-Bed Liner-WeatherTech Bugshield

 

There's allot more drag at 70 then 55
Most cars and trucks just start to over come
rolling resistance at about 55 after that it's all about over coming the wind resistance
and even thou the truck looks so aero dynamic the Cd of the truck has to be pretty high
I would guess it's about 38 to 40 Cd

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99 XLT SC 4x4 STYLESIDE ORP 5.4,AUTO & 3.73 POSI
MED. TOREADOR RED
EXTANG TONEAU,BED MAT,
K&N FILTER & WOOD DASH KIT

 

#1. It can't kick out of OD if it isn't in OD!

#2. At 70 mph, your truck is pushing considerably more air than it is at 55 mph. This is why the government lowered the speed limit to 55 back in the early '70's.

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2000 F-150 XLT Supercab 4X4,5.4,Off Road,Tow Pkg

 

Opie: She's in O/D at 70, the truck starts up in O/D, so when you hit 45-50 the o/d kicks in, if I start climbing a hill she kids out and around here it goes on and on like that, so I kick the o/d out before I get out of the driveway. So at 55 I hit 2K with o/d out, now I get up to 70, kick in the o/d and I'll hit 2K..At either speed I get 2K,but at 55 I get better mileage..Why, same rpm.

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2001 F150 SuperCrew II Lariat 4x4-4.6 V8-508A Lariat package-Dark Highland Green-Leather Captains Chairs-P/U Bed Extender-Rear Sliding Window-Skid plates package-Cab.Steps-Lower twotone paint-Power drivers seat/autolamp-Engine block heater-17" Chrome Wheels-Bed Liner-WeatherTech Bugshield

 

Rivers,

Even though the motor is turning at the same RPM, at 70 mph the motor is working harder to maintain 2000 RPM because of the increased wind resistance. When the motor works harder, it uses more fuel.

It sounds like your transmission is hunting gears when you drive on hilly roads while in overdrive. When this happens, you should turn the OD off until the road flattens out.

IMO, the 4.6L is not enough motor for a 4x4 SCREW with the ORP and 3.55 gears. I would suggest a 5.4L or 4.11 gears.

I had a '99 SCab 4x4 with 265/16 tires and a 4.6 auto, and I had the same problems as you. The truck hunted gears whenever the wind blew, or whenever is wasn't going downhill.

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2000 F-150 XLT Supercab 4X4,5.4,Off Road,Tow Pkg

 

Rivers,

Like the other posts state, it's all about load. If you stick your hand out the window when you are driving at 20 mph, the 'push' you feel against your hand represents the resistance of air dragging against your hand. Now try it at 55 miles per hour... much more drag.

If this still doesn't make sense to you because of the RPM thing, consider this:

If you pedal a bicycle at two pedal revolutions per second on flat land and then maintain that rate while going up a steep hill, will you feel like you are working much harder going up the hill ? Of course, because the load has increased (gravity pulling you back down the hill). Just like the increased load that develops by the air drag against your truck as your speed increases.

Trust me, if you're ever in Jeopardy of running out of gas in the middle of nowhere, SLOW DOWN, WAY DOWN for your best mileage (with proper tire inflation).

 

Hey Guys:
Thanks for the info, makes sense now. Was suck with the same rpm thing.

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2001 F150 SuperCrew II Lariat 4x4-4.6 V8-508A Lariat package-Dark Highland Green-Leather Captains Chairs-P/U Bed Extender-Rear Sliding Window-Skid plates package-Cab.Steps-Lower twotone paint-Power drivers seat/autolamp-Engine block heater-17" Chrome Wheels-Bed Liner-WeatherTech Bugshield