CarFilter: overdrive?

January 24, 2008 4:20 PM

John O'Connor, install my Oscillation Overthruster! Or not?

Bought a used Nissan Maxima, with automatic transmission, without owner's manual. Car has a button for something called "overdrive".

*with emphasis: I don't know what that is.

Yup, I read the previous thread from April, 2007- but unfortunately the (obvously very knowledgeable) answers are way over my head. Torque jolts and engine braking and variations in terrain... see above. (It's not you, it's me.)

All I want to know is- when I drive my car, is that button supposed to be on or off?

When I turn it off, a dashboard light appears saying "O/D OFF". The light is orange and attention-grabbing and suggests a "warning" light.

When I turn it on, no light.

My extremely simplistic interpretation of this is: on=good, off=bad.

If it factors in, I drive 75% city, 25% highway. If possible, I'd really just like to set it and forget it. Your advice appreciated.

posted by GuffProof to travel & transportation (14 comments total)

Off most of the time. On for freeway or other conditions where the transmission isn't frequently shifting. Hilly terrain will want it on. Simple as that.
posted by trinity8-director at 4:31 PM on January 24, 2008

you're right. the only time you would turn your overdrive off is in situations where your tires are slipping a lot, like in snow.
posted by lester's sock puppet at 4:32 PM on January 24, 2008

Leave it on(no light) unless you are towing something or you are in really hilly or mountainous terrain where your speed is kinda high but you are regularly descending and ascending.
posted by well_balanced at 4:33 PM on January 24, 2008

Wikipedia knows all:

An overdrive is a device which was commonly used on rear-wheel drive automobiles to allow the choice of an extra-high overall gear ratio for high speed cruising, thus saving fuel, at the cost of less torque.
...
For normal driving conditions, operation of the overdrive should be enabled only if the average speed is above 70 km/h (approx. 43 MPH).
posted by EndsOfInvention at 4:33 PM on January 24, 2008

And that button is there to turn overdrive OFF. Now, at this point, you may be asking yourself, "If I have an automatic transmission which chooses my gears for me automatically, why would I ever want to turn overdrive off?" That's a very good question, Mike! And in most cases, you don't want to turn it off.

Car Talk's take.
posted by drezdn at 4:34 PM on January 24, 2008 [1 favorite]

Turning overdrive off will give you more power and torque with worse gas mileage. On the highway where you're (presumably) driving a steady speed, you can turn on OD and get better gas mileage. If you need to pass someone you might need to turn it off. If your driving on a windy road or in stop/start city traffic, you can turn it off for better acceleration.
posted by doctor_negative at 4:36 PM on January 24, 2008

It's not just a performance issue. You can cause premature failure to the transmission by having OD on during city driving from too much shifting.

My older Max has the same thing and over time I've developed the habit of flicking the button to turn off OD when I first shift into drive (or reverse). A little annoying but not as much as taking it in for transmission repairs.
posted by trinity8-director at 4:41 PM on January 24, 2008

In any halfway modern car, the transmission computer should be smart enough to never engage the overdrive at all in city driving. I say leave the button alone and let the car figure it out. When "O/D Off" isn't pressed that doesn't mean "O/D On." It means "Turn O/D on when I need it, such as when I'm maintaining a steady speed on the highway."
posted by zsazsa at 5:01 PM on January 24, 2008

Leave the overdrive on. In normal conditions your car knows what gear to be in. If you find that it's shifting in and out of overdrive because you are towing something or are going too fast up a steep hill, THEN turn it off. Otherwise leave it on. Treat it as the car's "highest gear". There IS more to it, but that's all you really need to know.

BTW If you're driving in snow, you should be in a low gear to begin with (like 1st or 2nd), especially in an automatic.

Side note, I can't recommend highly enough the knowledge and "feel" you gain from becoming proficient at driving a manual transmission. You become more connected to your car and use more of your senses to understand what's going on (vibrations in your foot, sound of engine reving, g-forces when changing the accelerator position, smelling the burning clutch when you mess up now and then!). Though I must admit, I do enjoy being able to talk on the phone and eat a chili-dog at the same time while knee-steering in stop-and-go traffic when i don't have a pesky clutch pedal to push in.
posted by disaster77 at 5:36 PM on January 24, 2008

The term "overdrive" comes from the fact that when it's in operation, the wheels turn faster than the engine. (Or at least, that was the case in the original implementations of overdrive. The term may have been used later for cases where that was not true.)
posted by Steven C. Den Beste at 5:43 PM on January 24, 2008

Thank you and thank you! (Once for all of the no-nonsense advice, and once for not mocking the seriously automotive-impaired.) I appreciate it!
posted by GuffProof at 5:58 PM on January 24, 2008

I routinely turn off the overdrive when going down a hill on my commute. With the overdrive off, the engine handles a bit of the braking (the car won't "coast" as easily), helping to minimize wear and tear on the brakes. When I get to the bottom of the hill, overdrive gets re-enabled.
posted by gwenzel at 6:29 PM on January 24, 2008

Do what the owner's manual says to do. (OK, you don't have one. Might be beneficial to get one, they are actually useful.)

Everyone thinks they know what it means, but the overdrive concept is implemented differently in different vehicles.

Your conventional wisdom, light on=bad, is correct. Lights don't normally turn on to remind you that everything is ok and turn off when something is less than optimal.

In modern vehicles, turning overdrive off generally locks out the 4th gear and turns off the lockup torque converter. In english, that means the engine and the trans are spinning faster than they need to to accomplish the job at hand, creating more wear and burning more fuel.
posted by gjc at 7:18 PM on January 24, 2008

Seconding gjc: It might be a good idea to get an owner's manual. You never know when another question is going to come up!

You can get one from Amazon or eBay. Or you can read it for FREE on the web!!!
Here or here.
posted by exphysicist345 at 7:52 PM on January 24, 2008