A Family Medical History Filled With Diabetes, Heart Disease, and Cancer. As a young adult, I witnessed my beloved mother, the rock of our family, battle type 2 diabetes and the complications that come with it. She suffered from kidney failure, vision problems, and heart disease. After 33 years of fighting diabetes, she passed away in April of 2002. I miss her dearly.
Generally speaking, overdrive is the highest gear in the transmission. Overdrive allows the engine to operate at a lower RPM for a given road speed. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway.
OD saves strain on the transmission and I would speculate the drive train, also. Your car will coast more easily in OD and use less fuel. The only time I consider not using OD is when I am in town at speeds under 40 MPH. Purpose of Overdrive Overdrive is basically the cruising gear. In a car with an automatic transmission, you can drive in OD all the time. You should be driving in OD anytime you are traveling over 40-45 MPH. (This is the speed at which your car will automatically) shift into OD if you have it placed in that gear to start with. OD saves strain on the transmission and I would speculate the drive train, also.