overdrive is intended for highway use for better mileage.leave it on and your transmission will do all the work.even if its off it wouldn't damage anything.just your mileage would drop
Overdrive saves you gas, so keep it on, when its off it lets the engine rev higher, you should only turn it on when going up steep hills and don't want your transmission switching gears rapidly.
Overdrive saves you gas, so keep it on, when its off it lets the engine rev higher, you should only turn it on when going up steep hills and don't want your transmission switching gears rapidly.