Better to drive in OD all the time, or use D below 35mph?

[87mefull]

Is it better to shift into D for crusing below 40 mph or is it better to leave it in OD all the time? I know alot of older cars with OD transmissions it is recommend to do this, and I have seen this topic on another panther website also.

I don't know if it makes a difference in gas mileage or not, or if it will prolong the life of the transmission.

[Grand Marquis GT]

I got 3.08 gears, and hit OD only when i'm driving 50 or above..

of course, my TV pressure is high, so it won't let me do anything else

[phayzer5]

Its not the low speed in od thats the problem, it's the constant changing between D and OD. It creates excessive amounts of heat that will cause the clutches to burn up prematurely. If you can keep it in OD for a long period of time then do it. if your speed constantly changes, leave it in D until traffic smoothes out.

[Archangel]

I also have stock 3.08 rear gears and in city driving I use the overdrive only if I can hold 50mph for longer than a mile, otherwise I keep her in 3rd (D). While cruising a country road I'd just leave the shifter in OD and accelerate slowly, the 4th kicks in at about 42mph so I just get up to 45 and let it there - does miracles for my gas mileage.