I recently bought a Volvo 760 GLE -83 and its my first car with a automatic gearbox.. and I also noticed the "OD" button on it. And I know it stands for Overdrive.. but when and how do I engage the overdrive by pressing the button?
Is there anything to keep in mind? I read that they are quite fragile or something.. anyone? Its my second car ever, I've only gotten my drivers license last year.. So i'm not to familiar with cars yet.
And also, if you have any tips what to keep in mind when driving such a car.. if there is a typical problem with these cars that I should look for before its too late.. I know that the engine in mine (PRV-V6) has some mechanical problems in the ´83 model.

Thanks in advance,
Esa Salminen

The overdrive gear is taller than your 4th (or, in the case of an automatic, 3rd) gear, and thus allows the vehicle to maintain expressway speeds at relatively low engine RPM. Saves fuel and reduces engine wear 'n tear.

An automatic transmission will not shift into overdrive until the vehicle has reached about 45mph. Below this speed, the button on the shifter has no effect. Push the button in and overdrive is disabled (the amber "up" arrow in the instrument cluster is illuminated) until you push it again ("up" arrow goes off). You can use the button in this fashion to "lock out" the overdrive at speeds above 45mph. Useful for maintaining speed on steep grades, when towing a trailer, etc.

37 mph or so if it's an aw70/71 and you're not on the throttle and the car/transmission has warmed up. 45 roughly is when the lockup engages.
--
Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

The o/d is automatic: the button is there only keep it out of fourth gear (as when descending a long, steep hill).

Your PRV-6 suffers from inadequate camshaft oiling. You can limit any damage from this by keeping the engine internals clean (try a quality engine flush product, then draining the oil) and using a 0W-30 or 5W-30 full synthetic oil for good startup lubrication, film strength, and detergency.