Could someone explain to me what overdrive is?

[veggirl]

I have a 2005 Matrix XR (automatic). I noticed that under the gear shift that there is a little button that says "O/D". I decided to push the button while driving to see what happens. When I push the button, a light comes on that says "O/D OFF". I noticed that when I did it, the gear shifted higher while I was driving. I turned it off right away because I didn't like the yellow light ;-) What is this for? Does the car use more gas when O/D is off? What exactly IS O/D?? :-) (please pardon my ignorance, I did in fact search for threads about overdrive but people were talking about how much they like it, not what it was.)

Thanks in advance!!

[Clamhead]

Many cars use overdrive. It is simply an extra gear that lets the engine rev lower, thus improving fuel efficiency. A problem that can occur with this setup, however, is that the transmission can move between this higher gear and the one right below it resulting in the transmission shifting back and forth as you apply gas. This usually occurs on slight hills and is called "hunting" as the transmission can't seem to make up it's mind what gear it wants. Most manufacturers give you the option of turning off the overdrive (O/D), thus preventing "hunting". The result is that the transmission stays in the lower gear, prevents "hunting", but the engine as a result will rev higher and use more gas and potentially add more wear as it is working harder. You won't hurt anything by turning it off, but as a rule I always leave mine on unless I am experiencing that in-between condition that forces the transmission to "hunt" for the gear it wants.
Hope that helps.

[veggirl]

Thanks so much for the informative reply! :-)

How will I know when my car is "hunting"? I've noticed it shift gears temporarily on hills, from 3rd to 4th on the highway. (i'm guessing thats what the dial on the far left is telling me). Would it be better for my car if I turn off the overdrive when I see a big hill coming so that it doesn't have to jump like that? I usually drive at about 69/70 on cruise on the highway, and I notice the dial is just below the 3rd gear. I had thought that it would be higher than that on the highway, so I'm guessing thats the overdrive. So I'm guessing thats not bad for the car? Good for gas mileage? I want to treat this car the absolute best I can, I don't plan on buying another for 10 years ;-) I want to drive it in a way that will protect the engine.

[Clamhead]

You are right. The shifting of the gears up and down constantly is what is referred to as "hunting" as in hunting for the right gear to use. Your car is analyzing many different inputs from various sensors continuously to try to determine the correct gear to use to optimize fuel economy & performance. Unfortunately, there are some situations (mostly slight upward hills) where the car simply cannot make up it's mind. So as you move up the slight hill, you give it a little more gas, and the car downshifts to help you accelerate. When you reach the speed you want, you back off the gas, the car thinks it's done it's job and goes back up into a higher gear to give you back that fuel economy it's programmed to do. However, as the upward climb continues, you feed it some more gas, and the cycle repeats itself.

If you want to treat your car the best you can, leave the O/D button alone (so that it is not lit up on your dash) and let the car's mechanics & computers take care of it the way it was designed & engineered to do. In other words, don't worry about it. I have an 05 AWD XR that I also plan on keeping at least 10 years. I've had many cars with O/D and have never had a problem.
Just be sure to have the transmission fluid serviced per the manual and be sure to change that engine oil!!
Happy driving.

[Cyorke]

Just to let you know also the dial you see is not an indication of what gear the car is in. This is the tachometer and it tells the revolutions per minute that the engine is running. You will probably never really use it for much if you are jsut driving normal everyday driving. If you pay attention to it though you will notice that under normal driving conditions the transmission will shift gears at about the same RPM each time. If you were driving a manual transmission car you may use the tachometer to pick your shift points so as to suit your driving style. I have to agree with everyone else and tell you to jsut leave the car in O/D all the time and not worry about it. The only time I would think that you may want to turn it off is if you are in a very hilly area and have the car loaded, say you were on a trip and happened to be driving through the mountains. You can turn the O/D off while in the mountains jsut to help prevent it from hunting and then once you are out of the mountains turn it back on. And by the way ten years should be no problem for your car. I have had several Toyotas now and used to be a mechanic for a Toyota dealership. The one I jsut got rid of was a d 97 Corolla with 175,000 miles on it. I bought it new with less than 100 miles on it. Normal maintenance and that is it. Only took it back to the dealer one time for a problem and i did the repairs since I worked there. Even then it was ony an alignment issue. Follow the maintenance schedule in your owners manual and you will be very happy with your car for the next ten years or more I am sure.

[veggirl]

Thank you both so much for your help! I don't know much about cars, I always do the regular maintenance - oil change every 3000 for my old corolla VE. and I guess it will be every 5000 on the new matrix! The only things I knew how to change myself on the last car were the washer fluid and the air filter (and I changed my headlights myself, that was a PAIN!) ;-) But I always watched as work was done on my car, from brakes to fluid changes, to try to get to know it better. I want to do even better on this car. Thanks again for sharing your knowledge!!

[briangk_77]

Turning off the AT O/T isn't bad in the right circumstances. Turning it off slows the engine, which I find is helpful in bumper-to-bumper traffic or stop and go driving.

However, if you are cruising on the highway by all means turn O/D on. I think it may even go on automatically at certain RPMs.

[Batman]

OverDrive is the Gear on witch the Engine RPM are lower then the Wheel RPM......... meaning in 4 speed automatics your 4th gear is the overdrive......... Turning your OverDrive off means you are running in 3 gears......... In 5 speed Manual transmisions your 5th gear is your overdrive..... Hunting has nothing to do with overdrive..... Hunting happens in Autos not in Manuals........ you can turn OD off and still get hunting...... Reason is that in Autos the computer does the thinking for the shifting and sometimes it gets confused........ in Manuals unless you are confused then there is no hunting....... sometimes you can have double OverDrive........ Mustang COBRA, CORVETTE, VIPER have a double OverDrive tranny becuase they have the 5th and 6th gear over the 1/1 ratio of wheel and engine RPM........ basicaly to sum it up...... any gear over the 1/1 ratio of Engine to Wheel speed is OverDrive....... never turn OverDrive off.... it will save you gass..... to everyone it is just a useless buton and never touch it

[greywolf]

The button is also important for going downhill. You want the speed to be correct without using the brakes. That can require being in third gear or sometimes second. The O/D button push make third the highest gear and the 2 selection makes it second. Sometimes I really miss my manual transmission but, more often, my twice operated upon left knee gives thanks for the auto.

Turning O/D off has no effect in slow speed traffic. It only prevents upshifting to fourth which only happens at higher speeds.

[rated_w]

for me I use the O/D button when the RPM's drop way too low.. for example going up a hill and the rpm's drop under 1500, and the engine would sound like it's struggling..

I also use that sometimes when I'm slowing off the freeway.. using engine compression to slow down my car

[kano808]

hmm... i have always turned the overdrive off during 'city' driving and on during 'highway' driving. i have experienced that leaving it on does not necessarily save you gas. i tried something out... for one fill up i left my overdrive on and during another i used mine as described above. i found that the gas mileage is slightly better when i used the overdrive like above.

anyway, just thought i'd throw in my two cents...

[Wrin]

There is one instance where you should always turn off overdrive. Think of your transmission's gears as a set of pulleys -- all the gears before overdrive give you a gain of force -- torque at the expense of an increased engine speed. Overdrive is a 'backwards' gear -- meaning your engine spins at a lower speed, saving you gas, but you have next to zero torque.

If you're pulling a trailer or adding a significant amount of load to your vehicle in another fashion than a trailer (such as heavily loading down with cargo and a roof rack and other assorted racks,) your vehicle's automatic transmission becomes confused with how much torque it needs and also needing to save gas. This results in a shifting back and forth between overdrive and the next lowest gear, which negatively impacts performance. Lock out your overdrive to eliminate this condition. It will cost more in gas -- this is the price of hauling cargo.

If you do not turn off overdrive and are hauling a heavy trailer or are heavily loaded down with cargo, you run the risk of excessive gear 'hunting' which puts strain on your transmission. On flat terrain you could probably get away with it, however in hilly or mountainous terrain, you should lock out your overdrive (with the button) in order to obtain engine braking on downhills and to avoid hunting while going up the hill.

[Ukrainian102]

Aright plain and simple. Turning overdrive off is as simple as not letting your car use its highest gear. It's the same thing as if you shift down to 2 or L or w/e. Personally I dont know why they made it a button.

If your car is a 5-spd auto:

D, O/D on - car uses all 5 gears
D, O/D off - car wont shift above 4th gear
3 - car wont shift above 3rd gear
2 - car wont shift above 2nd
L - car will stay in 1st gear

If its a 4-spd auto:

D, O/D on - car uses all 4 gears
D, O/D off - car wont shift above 3rd gear
2 - car wont shift above 2nd gear
L - car will stay in 1st gear


Low gear gives more power, acceleration.
Higher gear is for higher speeds, more fuel economy.

Btw, I know you said you searched but there have really been at least 3 threads about this.