Over Drive?

Hi guys, I have a Sentra 95 automatic transmision.
The problem is that I am in MExico right now, actually is a little town where you drive not more than 30 Milles per hour or 25. I notice that on the freeway I get 500 milles with one tank on gas, but when I drive in the city the mileage reduces a lot. I would like to ask if I should or should not use Overdrive on the city driving at 25 milles per hour.
When should I use it.
What is it for?
How does it work on the transmission.

Thank you
Dasher

overdrive uses a diff final drive rato to get lower rpms for better mileage. you should not use it when driving under 50mph because it strains your tranny

It doesn't strain the tranny, all it does is allow the tranny to shift into the last gear. If you're going 25mph, it probably won't shift into 4th anyway. I'd leave it on all the time. Just shut it off when you are going pretty fast and need to slow down a little bit. It will downshift into 3rd and the engine will slow the car down for you, saving your brakes.

It might not be the same for Sentra's, but I remember on my brothers old Escort, it also seemed to lower the shift RPM's. Like with it off, you could go to near redline, but with it on, even with WOT it would shift about 500 RPMS sooner, and with light throttle it still seemed to lower the shift point from like 3500 RPM to 3000 RPM.

thats a possibility probably coded into the escorts engine management.
my old automatic SR-powered 99 sentra would shift at around 6200 (w/6700 redline) with OD on or off.
the only way i could get it to redline is if i manually shifted the gears.

but yeah listen to fugiot.
OD off just doesnt let the car shift to 4th gear, or if its in 4th, shifts down to 3rd and holds it.

Well, of course, because you disengage the 4th gear by pressing the button.

Well, of course, because you disengage the 4th gear by pressing the button.

I meant through all the gears, not just from 3rd to 4th.

I have to disagree. If you're in 3rd and shut-off over drive, it will stay in 3rd.

I have to disagree. If you're in 3rd and shut-off over drive, it will stay in 3rd.

Haha were on two different wavelengths here. I was saying that with it off, say with light throttle, it would shift from first to second to third at like 3500RPM's(not going into 4th because overdrive is off), but with it on, and light throttle it would go from 1st to 2nd to 3rd to 4th at like 3000RPMS. I wasn't saying that it would go to 4th with it off, just that it seemed to lower the shift point for every gear.

oh alright, I thought you were saying that it would downshift when you shut it off no matter what gear you were in.