Table of Contents

Summary

  • Overdrive signifies top gear/gears in a car that enable the engine to render better performance and fuel consumption.
  • In the automatic transmission, the overdrive is permanently on, and it can be turned off by pressing a button installed on the gear shifter.
  • When you turn overdrive off, a sign of O/D Off illuminates your car’s dashboard.
  • Overdrive mode is recommended to be used on highways and plane roads with less traffic where you can relatively maintain a speed of 60mph or above.
  • Improper usage of overdrive may cause the failure of transmission.
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What is Overdrive?

Overdrive is a car-operational system that allows you to attain more performance and experience optimized fuel economy. Engineer William B. Barnes is credited with the design of this marvelous invention. To understand the function of overdrive, it is important to understand its background first.

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Most of the cars manufactured during the 1960s to 1980s had three-speed automatic transmissions, which means they had 3 gears in their transmissions.
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Generally, the third gear used to be a direct drive. In direct drive, the input shaft, through which the engine is connected to the transmission, spins at the same speed as the output shaft, which further connects the transmission to the wheels.

By having the third gear as direct drive, earlier cars would have to exhaust their full engine power while driving on highways. Resultantly they would not only waste a lot of fuel but also cause disturbance to the passengers and drivers by making a lot of noise.

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This problem was solved by introducing some modifications to the car’s transmission. First, an additional gearing unit was attached to the back of the car’s gearbox box and was named 4th gear or overdrive.

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This additional gear made the input shaft spin slower than the output shaft, meaning that the engine has to work less to capacitate the wheels to run faster.
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Benefits of Using Overdrive

Reduces Engine’s Load

The overdrive functionality reduces the engine’s load, thereby lowering the wear & tear of the engine and transmission box.

Less Fuel Consumption

Gas prices are now about 10 times higher than their average level over the past decade. Since the continuous hike in gas prices increases the inflation rate, it is better to adopt fuel consumption techniques. When an engine rides with the overdrive gear, it will only require 1/3 less fuel. As a result, you can save a lot of fuel costs. It will also reduce gas emissions which is beneficial for our planet.

Increasing Engine Life

The overdrive uses only a few revolutions compared to lower gears. Therefore, less energy is required to complete the route, extending the engine life and giving less stress to your vehicle. In addition, other parts like the water pump, generator smog pump, A/C compressor, and alternator turn at lower RPMs when the engine uses overdrive.

Performance

According to recent research, vehicles with overdrive deliver 30% higher RMP than the traditional engine’s RPM [1]. Furthermore, a paper published in the Society of Automotive Engineers, Inc. concluded the application of overdriven gear (28-30%) is known to give considerable gains in fuel consumption and an imperative amount of reductions in the noise level [2].

No More Noise and Clattering

When your engine moves at lower RPMs, it will produce zero to little noise and a clattering sound. It lowers the noise, vibration, and harshness (NVH). Hence, you’ll experience a more relaxing and untroubled trip. If you’ve big vehicles carrying strong engines like SUVs or trucks, the overdrive feature will keep your ride smoother and more pleasant on the highway.
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How to Turn Overdrive On

In most automatic cars, the overdrive button is found on the gear shifter. The overdrive mode is permanently active in these cars, and you turn it off by pressing the overdrive button.

When you turn overdrive off, you will see an O/D off notification on your car’s dashboard. You can turn on the overdrive again by just pressing the same button.
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How to Use Overdrive Mode for Different Road Conditions

Overdrive mode is recommended when driving on highways or roads with less traffic. The only requirement is that you have possibilities in which you can maintain a speed of 50mph or above. The on-road situations where the overdrive mode should not be used are:

  • When your car is climbing up long, steep hills.
  • When you are on a road trip and want to drive slow to enjoy the trip.
  • When you are on the road with heavy traffic.
  • When you want to overtake a car.
  • When you are towing some heavy load.

Damages Caused by Improper Use of Overdrive

Although the overdrive feature in automatic cars helps you utilize a complete transmission range, improper use of O/D mode, especially in the cases mentioned below, may trigger severe issues.

  • Towing a trailer or large loads
  • Traveling at less than 50 mph
  • Propelling uphill
  • Driving in a town or city
  • Off-roading
  • Driving in terrible weather conditions

 

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Using the overdrive feature in all these scenarios will burn out the gearbox, and you need approximately $1500-$3500 budget to repair the broken parts.

However, the final price depends on the make, car model, local area, and extent of damage faced by the transmission.

States (U.S.)Cost of Replacing Gearbox
Alaska$800-1200
Texas$1800-3500
Virginia$800-1500
Hawaii$800-$1200
Ohio$1800-3500

Personal Experience

I live in Strood town, and my office is near Faversham, UK. It takes an average of 34 minutes to travel from Strood to Faversham by car. Therefore, I daily take the M2 route to reach my office. Earlier, I had an old manual transmission car consuming excessive fuel. Recently, I bought an automatic transmission car equipped with an overdrive mode. I didn’t know the advantage of this feature, but when I visited a local workshop, the mechanic advised me to turn O/D on when driving on the highway or Motorway. Since then, I’ve noticed that my car consumes less fuel and performs better.
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Conclusion

Overdrive mode makes cars fuel-efficient, engine stress-free, and saves drivers lots of money at the pump. It is recommended that you should turn overdrive on while driving on highways and plane roads with less traffic to have a better experience. It will protect your engine, gearbox, and transmission. However, the overdrive should be off when driving through slopes, hills, or mountains. Therefore, by having a good understanding of when to turn O/D on or off, you can experience considerable automotive benefits.

FAQs

The overdrive-off notification usually spotted in a car’s dashboard signifies that the car’s overdrive mode has been turned off. One can turn this mode on and off by simply pressing the overdrive button on the gear shifter. When overdrive is off, the vehicle’s higher gear/gears are locked, and the vehicle shifts to lower gears.

When you drive a car while keeping an overdrive on, you can save fuel, reduce engine wear and make the car less noisy on the highway than others. But it would help if you drove O/D off when you cannot maintain a speed above 60mph due to road conditions and circumstances.

If your O/D off light comes on and stays on, don’t worry. It indicates that overdrive functionality has been disabled by the vehicle, and now, the driver will have more manual control over the vehicle. In addition, it implies that the vehicle won’t shift to higher gears as it is limited to lower gears.

If you want to move your automobile to lower gear, overdrive should be turned off. It will enable your engine to consume fuel efficiently, along with better control over the engine brake. Turn off this feature when moving across hilly areas or carrying a heavy load.

The O/D off keeps the vehicle shifting from lower to higher gears in certain conditions, like driving through rolling mountains, moving down sharp grades, and transporting a heavy load. When O/D is turned off, the gearbox is limited to a lower bag to improve traction to provide safety and fuel consumption.

References

About Author

Andrew Ray

Andrew is an automotive technician with 10 years of experience mainly in American and Japanese cars, covering everything from routine vehicle maintenance and engine inspections to tire rotation.