Understandling Overdrive.

[MyTaurus8AChevy]

We are getting conflicting reports about when to use overdrive. According to a lot of people that we've talked to, overdrive is not needed in the city because it only works when you're going over 40. However we've noticed that when we use the standard drive gear that the engine has higher RPM's no matter what speed we're going, so if it's revving faster - wouldn't the engine be using more gas?

[Huney1]

"so if it's revving faster - wouldn't the engine be using more gas? "

Not necessarily because it won't be "lugging" or surging in and out of gears. I remember the Oldsmobiles had PRNDSL gears and the S stands for Super drive exclusively for city driving. Trying to think when that was and best I can come up with was in the mid to late 50's. I'm an old Dude, huh?

[MyTaurus8AChevy]

Originally Posted by Huney1

Not necessarily because it won't be "lugging" or surging in and out of gears.

But it's already in gear so if it's revving at 2.5K at say 40 MPH (for example) wouldn't it be using more gas than if it was going 1.5K at 40 MPH? All things being equal I would think that the faster it's revving over, the more gas it has to use

[shorod]

Probably your best bet would be to check your owner's manual for when it suggests NOT using overdrive. Typically, the only time you want to drive in something other than overdrive is if the car is heavily loaded or if you are climbing a long incline and the transmission continuously shifts in and out of overdrive. Any other time, you should be in overdrive. Again, this is typical, your owner's manual may suggest something different.

If you do not have the owner's manual, you can purchase one on eBay for reasonably cheap, or you can download one for free from the Internet. Way2old has posted the link numerous times, a quick search of the forum should yield you the link.

-Rod

[way2old]

100% agree with shorod. If you are going under a certain speed, or over a preset engine load, overdrive will not engage. If you want an owners manual, click here and click on maintenance tab, then owners manual. Enter information and download manual.

[MyTaurus8AChevy]

Originally Posted by way2old

If you are going under a certain speed, or over a preset engine load, overdrive will not engage.

This is what we thought too, but we can't answer why the RPM's are different (at the same speed) when we don't use it. That part doesn't make sense to us since overdrive should just be an extra gear it slips into around 40 MPH. Thanks for the link

[Millermagic]

I don't use it unless I plan on going over 45 or I'm in traffic. Otherwise, it would be shifting 3-4-3-4-3-4-3-4 all the time in traffic and that ain't good for it.

[way2old]

Mainly because when you shift out of overdrive you lose the 1 to 1 gearing.
each gear you go into that is higher, the RPM's will drop. Put car in second gear and check tack at 35 mph, then shift it to 3rd and watch tach. It will drop accordingly.

Originally Posted by MyTaurus8AChevy

This is what we thought too, but we can't answer why the RPM's are different (at the same speed) when we don't use it. That part doesn't make sense to us since overdrive should just be an extra gear it slips into around 40 MPH. Thanks for the link

[gbic1]

I dont know what car you have but any of my Ford products only have higher rpms at highway speed when overdrive is locked out. If you run in town below 45 mph then the trans should not kick into overdrive. If it does then it is shifting too early and will lead to problems sooner or later. Some people confuse overdrive and torque converter lock up. They are two different things. On a Taurus trans the overdrive is engauged by a band which speeds up a planet gear set and decreases engine rpms.