When to use overdrive in a 1993 Volvo 240 automatic transmissiom?

Keep the button for the overdrive engaged at all times and the vehicle will decide when it is needed. But if you prefer to determine when to use it yourself then its best to use it when your cruising the interstate. Its basically just a 4th gear that's designed to give you better gas mileage. If your "arrow" light is lit on the dash that means that your overdrive is off. If the light is off...your overdrive is on.