What size tires and what gears do you have? What speed are you at when it downshifts? If I start to go up a hill in o/d at 45 or 50 then it will more than likely want to downshift. If I'm going faster it'll usually stay in OD.

 

For me, it's at any speed. But then again, the small hills here may only be a 1/4 mile, but 5 or 6% grade. On the long 7 mile 5-7% grade, it actually holds it in OD. It's just the quick, little hills that slow it down fast and then it loses 5-8 mph and drops down and floors it. Also, just 265/70/16, which are Lincoln Town Car tires that weigh half of the Bridgestone Duelers I replaced.

 

Efficiency is not equal across the entire RPM range, so getting the engine into its more efficient RPM range saves fuel until you get up to the speeds where wind resistance becomes the more dominant factor.

 

Maybe mine is an exception, but when accelerating or maintaining speed, it stays in the 1400-1700 RPM range. Until it's up to speed enough for OD to kick in. It still defies the law of physics unless the transmission is not shifting when programmed to. All the manufacturers have optimized shifting to remain in that optimal middle zone where HP and torque merge-usually around 1500 rpms.

 

Lugging an engine can be just as bad for economy as revving too much. It all depends. My old explorer with stock tires and 3.27 gears got nearly 2MPG better when I stopped using 5th gear altogether. The factory doesn't always know best.

 

Even the owner manual say's to turn OD when coming up to a hill. Gear's are the problem, my 98 with 3:55's sucked.I had to turn OD off a 1/4 mile before the hill to get up it and mash the go pedal. My 2000 with 4:10s doesn't miss a beat and keeps speed(on those same exact hills, with no downshifting when in OD.

 

I agree...tuner helped my truck a lot. Even when it down shifts now it doesn't drop out of TC lock out, just od. So I use less rpm to climb the same hills.
BTW, I have my od set to come in at 41 mph at light to part throtle. With the tuner that has helped mileage even more.

Thanks again Sean.

 

My dad keeps trying to tell me that it's impossible to get worse fuel economy in a higher gear than a lower one. I disgree. He says every study always proves he is right. Can we get a better explanation maybe? Thanks

 

I already posted it, didn't I? The full explanation is long, but the short bit is that the greatest efficiency in most gasoline engines occurs at the RPM at which the engine makes right around 70% of its peak torque, which is usually right around 40% of red line RPM. Or right around 2,000RPM for our engines. Get too low in RPM and efficiency tanks due to pumping losses -- basically, making the engine fight to breathe through mostly closed throttle plates.

This stuff must be on the web somewhere. You might try finding it, printing some stuff out, and going off to win that argument with your pops.

 

My OD behaves better after SCT tune.....Do IT!