6G Celicas Forums

i recently purchased an automatic 97 celica ST hatchback. I have been wondering if most people leave there car in or out of overdrive? Any benefits to better mpg with overdrive??? what exactly does overdrive do?

Overdrive is basically like a 5th gear for automatics. I recommend keeping it on.

exactly...

unless for some reason you need alot of acceleration and your in like 4th gear...

over drive keeps rpms low which is want you want for more mpgs

This post has been edited by Add45: Oct 15, 2008 - 10:12 PM

i thought overdrive WAS 4th gear...

when overdrive is off it stays on third right? otherwise theres no way to get to third... since it shifts from 1-2-4 right?

Red joker is right. Overdrive gear is gear #4. Its called od because its gear ratio is less than 1, which means it delivers more rpm to the final drive (differential) gear than the rpm of the engine. Turn off overdrive when hauling heavy loads, to help preserve the 4th gear in your transmission. OD off will mean you can only use gears 1,2&3. Otherwise, leave it enabled (due to is nature of being overdrive, it is therefore the gear that is more likely to get damaged from friction or physical stress). The U140 transmission in some late model corollas is a rare example of a fwd trans that has no overdrive gear: it's 4th gear is ratio of 1. And yet, the U140 and the A140 use almost the same rpm as each other in each gear. Its able to achieve this by using a different final drive ratio.

This post has been edited by 3SGTE-auto: Oct 16, 2008 - 7:00 AM

Leave it on...it lowers RPM by about 1k in each gear.

This post has been edited by RickJamesBish: Oct 16, 2008 - 8:38 AM

im pretty sure overdrive is a run mode for the transmission where the torque converter locks with the flywheel (usually above 40 mph), thus giving you highway cruise mileage like a manual. I've never heard of it being a separate gear... Turning overdrive off allows the flywheel to spin faster than the torque converter, which multiplies torque but wastes gas.

i've been wrong before, but im confident with this assumption

That would be incorrect. Try turning off the OD button, and then count the times the car shifts gears as you accelerate on the freeway. Also, look up the definition of "Overdrive". Overdrive is defined as an transmission putting out output which is faster than the input speed (RPM).

The torque converter lockup is something that should occur automatically, and in the electronically controlled transmissions, this is controlled to occur when there the engine is not under heavy load and when at crusing speed.

3SGTE-auto is right

The basics of it is this, the Celica's automatic transmissions are 4 speeds
L = 1st gear
2 = 1st and 2nd gears
D = 1st thru 3rd gears
O/D = 1st thru 4th gears