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Overdrive or OD is the highest gear in the transmission in an automatic car. It brings the RPM of the engine down at a given road speed to facilitate better speed and fuel efficiency. It also helps your car to provide the best performance in higher speed cruising.
Usually, cars having this gear have a dedicated overdrive button. Switching it on means locking it out, not to engage it. When you push it, the transmission goes through all the gears and then limits the functioning within the rest of the gears. It means that there will be a downshift from the highest gear when you press the O/D button during driving at high speeds.
You should leave the OD switch on all the time for regular driving. Your car will automatically shift into top gear if necessary, regardless of your selection. However, there are some conditions when pressing the overdrive gear can improve the car’s performance.
When you’re speeding up
It’s the textbook condition for using the overdrive in automatic car. When you drive at more than 60mph (50mph in case of older vehicles), the RPM increases and the engine starts taking more and more strain. Turning on the OD will work like magic to take the pressure away from the engine and bring down the RPM.
However, don’t use it when you are speeding at less than 50mph or during city driving because the speed tends to be inconsistent there. The OD prolongs the life of your car’s engine and drivetrain only if you apply it wisely.
When you need to go downshift
The braking system has to take a lot when you drive downhill or get stuck in an extended traffic jam. Driving down a steep road requires you to put continuous pressure on the brake pedal while extended traffic requires sudden pushing of the pedal and speeding the car. If you use the OD in those situations, it will keep the RPM above idle without straining the brake and the engine.
What Damages can be Caused by Incorrect Use of OD Gear?
Turning on overdrive in automatic car will allow you to utilize the full range of the transmission. It also helps with the transmission life optimization and increasing fuel efficiency. However, if you use it incorrectly such as while towing a trailer, driving uphill, or speeding at less than 50mph, it will cause irreparable damage. It will burn out the transmission real fast which is a costly fix.
Source: Car from Japan
