Overdrive Queston
 

Hi all:

I am new to this group and this is my first post. (I own a 2000 Ford
explorer sport with the most basic no frill engine.)
Here the very newbie question: What purpose does the O/D serve?
Should I leave it on or off?
Someone told me that leaving the O/D on was essential for highway
driving but a waste of fuel for city driving. Is this true?
Does anyone actually know how the O/D works? Txs.

> wrote in message
oups.com...
> Hi all:
>
> I am new to this group and this is my first post. (I own a 2000 Ford
> explorer sport with the most basic no frill engine.)
> Here the very newbie question: What purpose does the O/D serve?
> Should I leave it on or off?
> Someone told me that leaving the O/D on was essential for highway
> driving but a waste of fuel for city driving. Is this true?
> Does anyone actually know how the O/D works? Txs.
>

For decades, all most all normal transmissions (automatic or manual) highest
gears were 1 to 1. That means that the output shaft turns 1 revolution for
every 1 revolution of the input shaft. Now it is uncommon to find a vehicle
that does not have overdrive.

Transmissions with "overdrive" have a higher (taller) gear, like .76 to 1.
That means that the output shaft turns 1 revolution for every .76
revolutions of the input shaft. That gear is over driven. The engine spins
fewer RPMs at the same travel speed, and torque is greatly reduced. For
almost all but the most extreme driving conditions overdrive results in
better fuel mileage.

I assume your transmission is an automatic? Generally the only time you
should have to be concerned about taking your transmission out of
"overdrive" would be if you were towing or hauling at or above you vehicles
GCWR Gross Combined Weight Rating. If your transmission is continually
hunting for a gear, shifting in and out of overdrive, you could use that as
an indicator to leave overdrive off.

CJ,

Thanks for the quick reply!
My transmission is indeed automatic. I shall leave the Overdrive on
--always, as I no towing at all. I live in drive in New Orleans, and
the heaviest driving I do is in the Appalachian mountain roads with a
loaded car. But from what I understand, leaving overdrive on is my
best bet unless I need an inordinate amount of torque.
Thanks again for your answer, and feel free to let me know if I somehow
misunderstood you!

When you are driving in the mountains, it is better to switch
overdrive off when coming down a steep grade as you get little or no
engine braking with it on. I also sometimes switch it off going up
grades if the transmission is shifting in and out of overdrive a lot.

On 10 May 2005 15:56:58 -0700, wrote:

>CJ,
>
>Thanks for the quick reply!
>My transmission is indeed automatic. I shall leave the Overdrive on
>--always, as I no towing at all. I live in drive in New Orleans, and
>the heaviest driving I do is in the Appalachian mountain roads with a
>loaded car. But from what I understand, leaving overdrive on is my
>best bet unless I need an inordinate amount of torque.
>Thanks again for your answer, and feel free to let me know if I somehow
>misunderstood you!

Interesting. I was wondering about the lack of breaking even when
coming down the rae 'hills' in New Orleans....
Plus the lack of overdrive would help to 'climb' the mountains too
--right?
THe rest of the time, I am leaving it on.

THanks to all for the info., I really apreciatte it.

> wrote in message
oups.com...
> Interesting. I was wondering about the lack of breaking even when
> coming down the rae 'hills' in New Orleans....
> Plus the lack of overdrive would help to 'climb' the mountains too
> --right?
> THe rest of the time, I am leaving it on.
>
> THanks to all for the info., I really apreciatte it.

Well, you seem to me to be putting on your coat and hat before checking to
see if it's cold outside. If you are going up and down hills then your
transmission will be "hunting" for the right gear (D or OD) and that's
probably not good for your transmission. Probably best to put in in D
unless you are going to be on a straight stretch for a while, over, say, 45
mph. If you are driving around the city not going over 35 then you'll
probably want to keep it in D. Your transmission will most likely let you
know at what speed it likes to go into OD so after you get familiar with
your car you'll have a good idea when to switch to OD and when to stay in D.
>

Ulysses, how does my transmission let me know what I need to do....(I
have an automatic if it matters)

Well this complicates things a bit... So if I stay under 35 and just
do city driving stay out of O/D
So concretly O/D should really be used when I am on the interstate, I
guess.

I realize these must be mega-newbie questions, and I must confess that
I am now more confused than ever....

"Ulysses" > wrote in message
...
>
> > wrote in message
> oups.com...
>> Interesting. I was wondering about the lack of breaking even when
>> coming down the rae 'hills' in New Orleans....
>> Plus the lack of overdrive would help to 'climb' the mountains too
>> --right?
>> THe rest of the time, I am leaving it on.
>>
>> THanks to all for the info., I really apreciatte it.
>
> Well, you seem to me to be putting on your coat and hat before checking to
> see if it's cold outside. If you are going up and down hills then your
> transmission will be "hunting" for the right gear (D or OD) and that's
> probably not good for your transmission. Probably best to put in in D
> unless you are going to be on a straight stretch for a while, over, say,
> 45
> mph. If you are driving around the city not going over 35 then you'll
> probably want to keep it in D. Your transmission will most likely let you
> know at what speed it likes to go into OD so after you get familiar with
> your car you'll have a good idea when to switch to OD and when to stay in
> D.
>>

Your transmission shifts into overdrive under 35 miles per hour? Maybe
with no load, but not if you are accelerating. Check that and get back to
us.

If you are not experiencing any gear hunting (Shifting in and out of
overdrive) don't worry about taking it out of overdrive.
The engine braking comments may apply to you, try it and see, that is a
simple downshift...

Otherwise, leave it in overdrive except for the most sever conditions.

"Otherwise, leave it in overdrive except for the most sever conditions.
"

Ok, I will, but why did another poster recommend I take it off OD if I
am doing city driving under 35 mph?

Is he wrong, or is this an accepted difference of opinion?

I leave my O/D on just about all the time, except going up OR down steep
grades. I also turn it off for quick high speed passing. We get great gas
mileage, 19 city/ 24 Highway 4.0 SOHC. I have 94,000 on her now. I attribute
this gas mileage to the way I maintain the vehicle and the use of Mobile
one oil.
In occasion I pull our POP UP when I do I seem to be turning off the O/D
more often but you will know when you need that extra torque, you'll just
feel it.

Searcher1