When To Use OD
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Freshman User
Joined: Dec 2014
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From: Deep in the MO Ozarks
When To Use OD
I have a 93 F250, and not sure of the purpose of the Over Drive function. Growing up, I was under the impression this was used when towing or when going up and down on hilly terrain to keep the Tranny from constantly shifting up and down. I was talking with someone about this and they said it was used for Hiway driving in order to get better gas mileage. In this case, Google was not my friend. So..what do you use O/D for? Thanks.
Senior User
Joined: Mar 2015
Posts: 450
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From: Merchantville, NJ 08109
Overdrive essentially switches to a higher gear, so the engine is not working as hard. It is supposed to save gas- however, as someone here pointed out in another thread, this is not always so... I tried his suggestion of turning it off when accelerating- it should automatically downshift, but mine does not seem to do so, and I get a much more effective acceleration when I switch overdrive off when starting out, or passing...
Scott
Scott
Postmaster
Joined: Nov 2011
Posts: 3,533
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From: SW Florida
Simple answer. Use overdrive for best fuel economy when cruising. If you're towing or otherwise making the truck work (heavy load in the bed perhaps) and/or are going up a hill or running at lower speeds, then shift out of overdrive (set OD OFF on E4OD/4R70W, shift to D on AOD, shift out of 5th gear on S5/M5OD) to get a better gear ratio for improved acceleration or maintaining your current speed.
So in other words overdrive is for the fast and easy parts of your drive. If you need to use much throttle to keep speed on, then get out of overdrive and you'll have a much easier time of it. You'll know when you should do this because you'll have a lot of throttle applied but the truck will barely be maintaining speed or accelerating.
So in other words overdrive is for the fast and easy parts of your drive. If you need to use much throttle to keep speed on, then get out of overdrive and you'll have a much easier time of it. You'll know when you should do this because you'll have a lot of throttle applied but the truck will barely be maintaining speed or accelerating.
Postmaster
Joined: Nov 2011
Posts: 3,533
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From: SW Florida
Note that the light indicates the control status, not actual transmission status. If the light is ON then shift into overdrive will never happen. But just because the light is OFF does not mean you are in overdrive, it just means that it's enabled and the computer will shift the trans into OD when/if conditions are right. Which would be throttle less than xx %, speed greater than or equal to xx MPH.
More Turbo
Joined: Mar 2011
Posts: 592
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From: Heber, UT
On the automatic transmissions, when the OD is on the computer adjusts shift points and will down shift early to keep rpms at their minimum in each gear. With the OD off it will maintain higher rpms in each gear before down shifting and will not shift into the OD gear. I usually turn my OD off for driving around town empty, towing a trailer (depending on the size anyways), and hauling alot in the bed.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
The use of OD is going to be vehicle specific unfortunately because Ford used several different auto OD transmissions and also used a very wide range of axle ratios in these trucks.
Both of the computer controlled transmissions(E4OD and 4R70w) are rated for towing in OD so there is nothing wrong with just letting the computer make the decisions unless you find yourself in a situation where the trans is repeatedly shinting into and out of OD frequently, then it's better for the trans if you disable OD.
The AOD is not rated for towing in OD and the early 1/2 ton trucks this trans was installed in were also dumping grounds for some very unsuitable axle gearing, that is unsuitable for a truck and for one with an OD trans. If you have one of these with 3.08 or 2.73 gears you should never use OD unless exceeding 70mph, this will extend trans life and actually produce better gas milage with EFI equipped vehicles.
Both of the computer controlled transmissions(E4OD and 4R70w) are rated for towing in OD so there is nothing wrong with just letting the computer make the decisions unless you find yourself in a situation where the trans is repeatedly shinting into and out of OD frequently, then it's better for the trans if you disable OD.
The AOD is not rated for towing in OD and the early 1/2 ton trucks this trans was installed in were also dumping grounds for some very unsuitable axle gearing, that is unsuitable for a truck and for one with an OD trans. If you have one of these with 3.08 or 2.73 gears you should never use OD unless exceeding 70mph, this will extend trans life and actually produce better gas milage with EFI equipped vehicles.
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Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,722
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From: SE Florida
What confuses many people is the term overdrive. All overdrive is is a gear ratio that is less than 1:1. It is just fourth gear in a four speed transmission.
When the OD is turned off, the light is turned on. In this configuration the transmission can only shift 1-2-3. When the OD OFF light is NOT on the transmission can shift 1-2-3-4.
You can leave the OD on (light OFF) any time the transmission is not frequently shifting between 4th and 3rd gears. This will be at least 95% of your driving.
When the OD is turned off, the light is turned on. In this configuration the transmission can only shift 1-2-3. When the OD OFF light is NOT on the transmission can shift 1-2-3-4.
You can leave the OD on (light OFF) any time the transmission is not frequently shifting between 4th and 3rd gears. This will be at least 95% of your driving.
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Joined: Feb 2013
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From: Roseville, MN
Expanding a little on what Mark said, don't think of it as overdrive, just think of it as the next higher gear.
When do you use a higher gear? When you want the engine to be running slower at the given vehicle speed. That generally is because you want better mileage, less noise, or the ability to go faster than you are. If anything like that is true and you are in 3rd gear ("drive") of an automatic or 4th gear of a manual trans, then you should upshift.
When do you use a lower gear? When you want the engine to be running faster at the given vehicle speed. That is generally because you want more power, or because you are starting to lug the engine. It can be to get better mileage if you are getting too far below the engine's power curve. If anything like that is true you should downshift.
When do you use a higher gear? When you want the engine to be running slower at the given vehicle speed. That generally is because you want better mileage, less noise, or the ability to go faster than you are. If anything like that is true and you are in 3rd gear ("drive") of an automatic or 4th gear of a manual trans, then you should upshift.
When do you use a lower gear? When you want the engine to be running faster at the given vehicle speed. That is generally because you want more power, or because you are starting to lug the engine. It can be to get better mileage if you are getting too far below the engine's power curve. If anything like that is true you should downshift.
Senior User
Joined: Mar 2015
Posts: 450
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From: Merchantville, NJ 08109
With mine, I started using the O/D as a defacto 4th gear manual shift: I have been switching it off for speeds from stop to about 50, then engaging it... I have been getting better acceleration from the truck since i started doing this earlier this week...
I have driven her to work all week, and think her mileage may be improving as well...
Scott
I have driven her to work all week, and think her mileage may be improving as well...
Scott
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,722
Likes: 2,648
From: SE Florida
With the OD off from a start the trans shifts 1-2-3, then will shift to 4 when you turn on OD again.
With the OD on from a start the trans shift 1-2-3-4.
So are you only getting the better acceleration in third gear at speeds about where it would normally shift to 4? Any speed below that the transmission is doing exactly the same thing.
Senior User
Joined: Mar 2015
Posts: 450
Likes: 3
From: Merchantville, NJ 08109
Let's see how this works.
With the OD off from a start the trans shifts 1-2-3, then will shift to 4 when you turn on OD again.
With the OD on from a start the trans shift 1-2-3-4.
So are you only getting the better acceleration in third gear at speeds about where it would normally shift to 4? Any speed below that the transmission is doing exactly the same thing.
With the OD off from a start the trans shifts 1-2-3, then will shift to 4 when you turn on OD again.
With the OD on from a start the trans shift 1-2-3-4.
So are you only getting the better acceleration in third gear at speeds about where it would normally shift to 4? Any speed below that the transmission is doing exactly the same thing.
Scott