The advent of automatic transmission was a huge step forward in improving driving comfort. But the first prototypes of such boxes were imperfect, so designers are constantly working to improve their performance characteristics, while at the same time taking care of reducing fuel consumption.
Currently, the most popular is a four-speed automatic transmission, since it has a limited number of operating modes, which makes it much easier for beginners to master the skills of handling this unit.
However, the presence of additional modes to the basic ones is not something exceptional - almost all simple automatic transmissions are equipped with non-standard modes used in appropriate situations. The Overdrive mode can hardly be called standard, but it is not exotic either, since it is present on so many boxes.
Let's consider why it is needed and in what cases it is used.
Overdrive Functions
To understand what Overdrive mode means, you need to understand what tasks the designers set when creating it. It's no secret that an automatic transmission has a much more complex design than its mechanical counterpart. Therefore, in general, the reliability of such a transmission is initially lower, even purely theoretically. This means that the developers are faced with the important task of reducing the operational loads on this unit. One way to solve this problem is to add gentle operating modes, allowing you to increase the overall resource of both the transmission and the power unit. Overdrive mode is just such a tool.
Its main purpose is to select the most optimal mode of movement, taking into account the current speed of the vehicle and the magnitude of the crankshaft torque. Enabling the mode can significantly reduce the load on the mechanical components of the transmission, which theoretically should also reduce fuel consumption.
A typical automatic transmission is equipped with four stages, with the third speed considered direct, since its gear ratio is equal to one. In a manual transmission, its analogue can be called fourth gear.
If the automatic transmission has an Overdrive mode, then there is also a fourth speed, indicated by O/D symbols. In a manual transmission, its analogue is fifth gear with a gear ratio less than one. This means that this gear is an overdrive, that is, the transmission output shaft rotates at a speed exceeding the crankshaft speed.
On cars equipped with a manual transmission, the optimal mode for engaging an overdrive gear is to achieve speeds of about 80-90-100 km/h. At the same time, fuel savings are achieved by increasing the output torque. In an automatic transmission, the driver has virtually no influence on the gear shifting process, which is why the O/D button appeared, which allows you to use the upshift mode.
The button itself has two location options:
- directly on the selector;
- separately on the panel or steering column (quite rare).
When the mode is enabled, the automatic transmission will switch to 4th gear when the car reaches high speeds, or when the driver slightly presses the accelerator pedal. As soon as the high gear is engaged, the torque converter will lock.
But since the automatic transmission is operated in completely different modes than the manual one, in reality, switching to fourth occurs at much lower speeds, about 50 km/h.
In this regard, many car owners have a question about how advisable it would be to use the Overdrive button on an automatic transmission when driving primarily in urban conditions. Let's try to understand this issue.
Why doesn't the Overdrive button work?
The overdrive button may not work for a number of reasons. Like any other mechanism in a car, the overdrive button on an automatic transmission has its own resource, and can fail during intensive use, simply due to physical wear and tear (which is extremely rare in practice).
The most common reason for the failure of the O/D button is broken wires or poor contact on the connector going to the button. In this case, the problem can be resolved by disassembling the automatic transmission shift knob and restoring the integrity of the wiring.
If everything is fine with the button itself, the wires and connectors are intact, then the problem may be much more serious. In particular, you should check the overdrive sensor and diagnose the automatic transmission itself.
Overdrive in the city
Should you use a higher gear when traveling within the city? The opinions of experts here are divided, and the arguments of both sides sound quite convincing and reasonable, so you will have to make a decision on your own.
Proponents of turning off this mode explain their position as follows: road conditions in modern cities are such that it is impossible to move at a uniform and relatively high speed for any length of time. This is hampered by dense traffic and the presence of adjustable traffic lights, which greatly influence the speed limit on certain sections of the road. This means that the box has to constantly switch, and when the mode is on, this will lead to frequent locking of the torque converter. And this means accelerated wear of this unit and an increase in fuel consumption that occurs out of the blue.
Adherents of using Overdrive believe that the last argument of their opponents is untenable. The point is that, regardless of whether the O/D button is turned on or off, the automatic transmission will still have to use frequent gear changes. And in this case, fuel consumption will certainly increase compared to driving on the highway, regardless of the time of year and the preferred driving style of the car owner. Therefore, even a short-term upshift will help save fuel.
Using the OD mode of an automatic transmission in practice
To understand how to use the overdrive mode in the city, let's look at a specific example. The car can move uphill in traffic, constantly changing speed from 30 to 70 km/h.
If overdrive mode is turned on, the automatic transmission will shift to all gears (1,2,3,4). Also after accelerating to 40-50 km. The torque converter will be blocked if the driver does not press the gas pedal very hard.
Let's imagine that the car accelerates to 60 km/h, while 4th gear is engaged and the engine speed is low. If at a certain moment you need to accelerate, you should not expect a sharp response to pressing the gas pedal, since fourth gear is engaged, and there are not enough revolutions for intensive pickup in this gear.
All you have to do is press the gas harder, the kick-down will work, a sharp downshift will occur and acceleration will begin. Further, this situation is repeated many times. Naturally, in this case, comfort is significantly reduced, and the gearbox itself wears out faster and more intensely when constantly changing gears.
If you turn off overdrive, under load the car will move in a maximum of 3rd gear, and it reacts more responsively to pressing the gas pedal, the engine speed is higher, and without shifting down there is enough traction for acceleration.
However, you should not assume that disabling 4th gear will lead to an increase in fuel consumption. The fact is that the forced use of the kick-down mode if O/D is turned on ultimately leads to greater fuel consumption during city use.
It turns out that you need to be able to use the overdrive mode, turning it on and off depending on certain conditions. As mentioned above, it is better to turn off overdrive:
- if active driving is practiced at low speeds;
- on long descents/ascents;
- if the pace of movement is constantly changing;
- for comfortable movement at speeds up to 50 km/h;
- when towing a trailer/carrying cargo in a car;
- during prolonged overtaking at medium speed;
By the way, regarding the last point, you need to remember that turning off overdrive will cause the engine speed to increase sharply, and the increase can be right up to the cutoff.
You also have to turn on/off the O/D mode with a separate button, and it is extremely unsafe to be distracted from the road at speed and, especially, while overtaking. For this reason, when overtaking on the track, it is optimal to use kick-down rather than overdrive.
The only exception is safe overtaking of relatively slow-moving vehicles. In this case, the overdrive is turned off in advance, only then does overtaking begin; if necessary, kick-down is also activated in parallel with the overdrive turned off.
Finally, we note that regardless of the type of transmission and the available modes of its operation, the main thing is to be able to correctly predict the situation, take into account road conditions, and the operating features of the automatic transmission on a particular car model. Only after making sure of complete safety can you overtake, change lanes and other maneuvers.
How does the automatic transmission work when 4th gear is engaged?
If the display indicates that Overdrive is turned on, the car will sequentially switch from the first to the fourth stage when accelerating. But once overdrive is reached, the torque converter will be locked up. This moment is clearly noticeable thanks to a slight push - it is by this that most drivers determine the moment the car switches to an overdrive.
Strictly speaking, this is not an entirely correct judgment, since the cause of the push is not the transition to Overdrive, however, at high speed, locking of the torque converter can be caused by this very reason. Unlocking of the GT occurs when the car is braking, along with the automatic transmission switching to lower gears.
Why enable and disable O\D mode
For clarity, you should consider an example in order to understand the importance of turning off and turning on overdrive in urban conditions. If the car is moving on a hill, often changing speed, when overdrive is turned on, a significant change occurs in the operation of the automatic transmission
During acceleration, all gears will be switched sequentially, and the torque converter will have time to lock up.
If a car is moving at minimum speed at a speed of 60 km/h, but there is a need for sharp braking, and then an increase in speed, without overdrive the engine will not be able to instantly respond to such changes. Therefore, the overdrive mode should be used when driving at unstable speeds, as it significantly facilitates the driving process.
It is also important to remember when it is prohibited to use this mode and always follow road safety rules
Overdrive mode and fuel consumption
During our introduction to the operating principle of Overdrive, we stated that its use saves fuel. As practice shows, this effect is rather demonstrative in nature, indicating that less fuel is actually consumed.
That is, the driver, with proper use of the mode, which involves turning it on/off in a timely manner, can save a little, but you should not count on a significant reduction. So any myths about the influence of Overdrive on fuel consumption should be taken with a considerable amount of skepticism. There are savings, but they are insignificant.
Pros and cons of Overdrive mode
Although overdrive in automatic transmissions appeared relatively long ago, passions about this issue still rage to this day. Some consider it a useful acquisition, others are against using Overdrive. Let's try to sort everything out and start by listing the advantages of having this mode:
- the overdrive mode allows for smoother operation of the power unit at low speeds;
- when driving for a long time in the speed range of 60-100 km/h, you can save a considerable amount of gasoline;
- the automatic transmission, and with it the engine, wear out to a lesser extent;
- During long trips, the Overdrive mode provides increased comfort for the driver.
But there are also many disadvantages:
- a large number of automatic transmission models do not have an O/D shutdown button, so the overdrive will always be engaged, even when driving at high speed does not last long;
- if the car is used primarily within the boundaries of a large populated area, Overdrive will be an almost useless option;
- frequent switching on/off of the 4th stage of the automatic transmission leads to an increase in the number of torque converter shutdowns, which can hardly be called a positive thing;
- When the Overdrive mode is turned on, it becomes more difficult to control the car in difficult road conditions (for example, icy conditions) - engine braking becomes extremely difficult.
From the above we can conclude that the use of ML is not always good. Fortunately, this transmission mode is not standard, so the driver can decide when to use it and when not to use it. In any case, its absence reduces the functionality of the automatic transmission.
But even without it, to be completely honest, you will lose very little.
How to use overdrive on an automatic transmission?
To date, there is no clear explanation of how to use this function. This is due to the large differences in driving situations and engine power in different cars. Drivers enable and disable this feature based on years of experience, but what should newbies do?
This question can be answered by experts who give the following recommendations on this matter. Here are the following cases when you need to disable O/D:
- When driving on long descents or ascents . It’s completely understandable why you would do this on climbs, but why turn off overdrive on the descent? When you engage a higher gear, the car coasts better, which means that braking efficiency decreases, which has a great impact on traffic safety. That is why, on descents, overdrive must be turned off.
- When driving in a dense flow of vehicles , where the speed of movement periodically changes.
- When overtaking at a speed not exceeding 90 km/h . Although the opinion with overtaking is controversial. On the one hand, increasing the speed helps to quickly complete the maneuver, but on the other hand, it is no longer safe to remove your hand from the steering wheel to press the button, although overdrive can be turned off by sharply pressing the gas pedal all the way. In addition, if you do not know your car, you can bring the engine speed to the red zone when reducing the gear, which will accelerate its wear. Everything will depend on your experience driving this car.
The question of the application of this function in the city is also controversial. It all depends on the engine response and specific driving conditions. Therefore, there is still no clear explanation on this matter.
Where should overdrive be used? When driving on the highway, as well as in any places where a sufficiently high speed is allowed.
Overdrive analogue
Drivers with minimal experience should not use Overdrive - their experience is clearly not enough to understand in which cases the button should be pressed and when this should not be done. For beginners, any road situation is difficult, so decisions need to be made quickly; any delay is fraught with trouble. Including those related to the inclusion of ML mode. So you should rely more on the automation controlled by the on-board computer than on your own little skills.
The same applies to the Kick Down mode, which is a kind of antagonist to Overdrive. Although it is common for beginners to believe that these are related modes. In fact, this mode has no analogues, and you need to use it skillfully.
