overdrive and fuel economy

[EK1]

hey,

i drive a stock automatic 1989 camry. im just wondering is it more fuel efficient with the overdrive button on or off. thanks

[lateralus]

its more fuel efficient to drive with overdrive on. reason being is the transmission will naturally find the lowest ratio gear so there is less load on the engine at lower revs.

however, it does depend on what sort of driving you do. going through very hilly areas its more efficient to drive with o/d off, as theres less gear changes and youre not working the engine as hard to carry the same load (eg. throttle 1/2 way down in 3rd gear at 2500rpm puts more load on the engine, as compared to throttle 1/4 way down in 2nd gear at 3500 rpm). but obviously on the highway at 100km/h on a flat road, its more efficient to have o/d on.

and also, with some lower speed suburban driving (eg. 50km/h and lower) there isnt much difference as the car will rarely select the lowest gear ratio, and will usually stay in 3rd or so (assuming its a 4spd transmission)

Edited March 2, 2010 by lateralus