Unless the 3rd speed is already an overdrive, yes. What matters is the highest gear keeps your engine RPM around 2500 rpm at around 70 mph.
You have to use it when you are driving in mountain areas where to have high speed is not a good idea. The overdrive function does allow the transmission to switch to higher gears.
Under normal conditions when driving at highway speed should allow the transmission to shift into overdrive.. Assuming automatic, if the O/D indicator is on when accelerating from a stop, and in most cases during stop and go driving (when transmission has not settled into high gear, or under heavy load), it should not be on. This should apply to literally any vehicle with automatic & overdrive. If it is on when an automatic transmission has not reached high gear, it would be a symptom of an electrical or sensor switch malfunction.
highway driving
In Nissan Sunny (and some other cars too), overdrive is ON when the button is DEPRESSED and there's NO LIGHT in the dashboard. The automatic transmission will utilise all the 4 forward gears (the 4th gear being the overdrive that helps in fuel economy -- similar to 5th gear in a manual gearbox). This is the recommended setting for normal driving. When the button is NOT DEPRESSED, you turn OFF overdrive, and the indicator LIGHTS UP in the dashboard. In this mode, the automatic transmission will NOT shift into 4th gear.
Overdrive in Subarus, like just about every car with an automatic transmission built in recent memory, is built into the routine working of the transmission. Your transmission selector, if it's like mine, has a "D" for drive then the next digit down is a "3". Choosing the "D" allows the vehicle to access overdrive when appropriate. Driving with "3" as your chioce does not allow the overdrive to work. --Ken
Your transmission might automatically shift out of overdrive while driving on the interstate because of low transmission fluid. This issue might also occur because of a bad transmission sensor or overdrive sensor.
Generally speaking, overdrive (O/D) is the highest gear in the transmission. On most cars the automatic transmission has 3 speeds and Overdrive (forth speed). Overdrive allows the engine to have less rpm with higher speed in order to have better fuel efficiency. When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 30 - 40 mph depending on the load). When it's off, you limit transmission shifting by third speed.In normal driving condition the overdrive should be always on.You may need to switch it off when driving in mountainous area or towing a trailer.[The automatic transmission automatically shifts from OD to the 3-th gear when it feel more load. When it feels less load it shifts back to the O/D, but under certain conditions, e.g: driving uphill or towing a trailer, the transmission can not decide to stay in OD or to shift into 3-th speed and it starts to shift back and forth. That's the time you may switch it off and help the transmission to decide.] .You also may need to switch it off when you want to slowdown using the engine braking, for example, driving downhill. [For more details, check your owner's manual]
Transmission Problems, you shouldn't be driving with this on!
Overdrive ON is the normal position But if you are towing something or driving in hilly country where the transmission is constantly shifting from overdrive to drive , then you want to switch the overdrive off
It's not recommended to use overdrive on a constant base. It stresses too much the engine as well as transmission.
your overdrive unit is probably shot. that is the fourth gear or drive as you call it. they have had lots of trouble with all overdrive automatics in the states. your opel is a GM design.
I had a 1993 several years ago and I think I got about 26 MPG combined city and highway driving.