1) Should overdrive be used over 50 MPH?
2) Can one shift into overdrive while being in motion, or will it mess up the engine?
3) Does overdrive really make that much of a difference? If so, more with in town or highway?

For reference, I have a 2005 Hyundai Accent 3-Door pretty much bare minimum in it. It has a salvage title, but if the people would have inspected it properly when fixing it then it wouldn't. I used to drive a Pontiac Grand Am 1995, so I never had overdrive before..and it had really crappy gas mileage for a 15 gallon tank. Just checking this out before I screw around with it much, and please don't tell me to RTFM, please.

Thanks!

 

You can shift into and out of overdrive at will, no problem there. Basically, use it all the time except for times when you feel you need a little more power/acceleration, or if you're at a speed where the transmission is "hunting" (frequently shifting between the top gear and the next one down).

 

I'm assuming you have an automatic, because the term "overdrive" isn't used with manual transmissions except when talking about gear ratios.

Anyway, yes, the overdrive should almost always be on. In fact, it is most beneficial when you are driving over 50 mph.

Think of the overdrive as being a higher gear for more fuel-efficient driving - similar to having a 10-speed bike versus a 3-speed bike. What the overdrive does for you is that it allows the engine to turn slower for any given speed. If you're going 50 mph with the overdrive on, the engine might be at 2500 rpm. Wiith the overdrive off, it will be doing 50 mph at maybe 3100 rpm (and using more fuel). So, normally, leave the overdrive on and the automatic transmission will choose which gear to use and when.

The only time you would turn the overdrive off would be, essentially, to drop down into a lower gear for more passing power or if you're climbing a hill. Also, as mentioned above, if the transmission is "hunting" (going back and forth between gears - which you can feel), then you might want to turn overdrive off until you're on a more consistent type of terrain.