Newb question

[the_mavsman]

Hey, how's everyone doing.

I just wanted to ask is overdrive on by default? The reason I asked is when I press the OD button it displays 'OD Off' on the dash while the instructions manual clearly says that OD is off by default. I am not good with cars so excuse me if this sounds like a retarded question.

I drive a 02 Corolla Sedan Conquest by the way if anyone's wondering.

[Leroy]

From what I can gather, you want overdrive on for busy city driving - keeps the revs up so you can zip around, and take the odd hill etc...

When you hit a highway cruising speeds, overdrive should be turned off - easing the workload of the engine and thus saving you fuel.

(I am also not good with cars - this may be a retarded answer =p)

Edited April 3, 2008 by Leroy

[Jaaassseeee]

I'm pretty sure its the other way around

[Kenneth]

What i find with O/D is actually...

How auto trans rolla have 4 gears.. L being 1st gear, 2 being second gear then it jumps to D which sits @ 4th gear when it gets up to it.. so to get back to 3rd gear and give ur car a little kick in the ***** to pick up some speed u turn on O/D which brings the car back to 3rd gear...

I find that you should never leave O/D on while driving simply because it makes the car feels rly odd not hitting 4th gear (no matter where u drive) just do it when u need to overtake (if you are going to o/take at speed below 100kph.. u are better off putting it to 2nd gear :P)

EDIT

LOL omg.. did i just put everything the wrong way round LOL.. lets change it =.=

Edited April 3, 2008 by Kenneth

[Hiro]

I'm pretty sure its the other way around

Correct

Ok people, here's what it is

In a standard 4-speed auto, there are 4 gear ratios. 1, 2, 3, 4. If you put transmission in L, it will stay in first gear. If you put it in 2, it will not shift higher than 2nd, but will drop to first if necessary. If the car is in D, and overdrive OFF, the car will use 1st, 2nd and 3rd as necessary. When you turn overdrive ON, 4th gear becomes available.

The reason it is called overdrive is because 4th gear is a gear ratio less than 1:1 in the gearbox. I don't know off the top of my head what the actual ratios are, but they'll be something like this

First

3.5:1

Second

2.7:1

Third

1.8:1

Fourth

0.8:1

It is called overdrive because the engine is overdriving (ie spinning the output much faster than the input) the transmission. Greater than 1:1 (ie first, second and third) are called underdrive, as the output is spinning slower than the input.

Now, the reason there is an O/D off switch is threefold.

1) In city driving, you're not going to get into fourth that much. Thus, to stop the transmission going into fourth and then kicking back to third because speeds aren't high enough and the engine is bogging down, turning O/D off will keep the transmission in 3rd or lower.

2) In towing conditions, the added weight and drag of the towed vehicle (ie trailer, caravan etc) means that the car will struggle to pull in 4th gear. Thus, overdrive is turned off to keep the revs up.

3) In hilly high-speed driving (ie open road highway, bits of the freeway), the engine will happily cruise in fourth but will have to kick back to third for hills. Now, if the hill is long enough, the car may get enough speed back up for the transmission to shift into fourth. It'll then bog down, and shift back to third, and this process will continue. This is called HUNTING, because the gearbox hunts up and down between the ratios trying to find the best gear. Turning overdrive OFF will keep the transmission from shifting into fourth, and make it easier to get over the hill

In most other conditions (ie flat open road, >70km/h), it is best to turn overdrive ON so that the transmission can shift into 4th and achieve maximum possible fuel economy.

Here endeth the lesson

[the_mavsman]

Thanks for the help guys.

That was a fair bit of knowledge I just absorbed. But not to be rude or anything, I still want to know why when I turn overdrive, it says OD off on the dash?

Edit: wait nevermind, I just figured it out. So over drive = 4th gear is used and over drive OFF means it only uses 1,2,3. Woah so I was wrong for all those years.

Edited April 3, 2008 by the_mavsman

[pinzvidz]

Thanks for the help guys.

That was a fair bit of knowledge I just absorbed. But not to be rude or anything, I still want to know why when I turn overdrive, it says OD off on the dash?

Edit: wait nevermind, I just figured it out. So over drive = 4th gear is used and over drive OFF means it only uses 1,2,3. Woah so I was wrong for all those years.

Gheeeezzz... I'm glad you don't own a Mazda2 (or earlier Mazdas with the "Hold" button instead of "O/D Off". That would well and truly confuse the sh!tter out of ya.

[Leroy]

Awesome... everyone learns something!

[Seano]

Awesome... everyone learns something!

Haha I love the hold button, had a mate in the near the central coast who didn't know what it was but after I showed it to them they have never gone back from a abusing that poor little Laser's hold button.