will it mess up your engine if you drive with the overdrive on all the time.

 

No! Who told you that?

 

I was just wondering what the Overdrive button is for

 

overdrive is good.

 

Without overdrive you wouldnt be able to go over 60mph and your rpm's would be over 5k..

 

You can go over 60. You will just be running at higher rpm (no such thing as rpm's) - it is basically preventing you from shifting into 4th (the overdrive gear). The only reasons to turn it off are for keeping the engine running hihger for passing power or in a hilly area where you want to prevent it from shifting back and forth. Also useful for towing sometimes - but not sure if anyone uses their GS for towing!

 

start at 50mph with OD on go up to 70
start at 50mph with OD off go up to 70

then
start at 50mph with it off, turn it on at about 65-70 and it excellerates faster with lower revs. (I think the OD in the GS is more then just a "4th gear" because in 2nd and 3rd revs have changed when I hit it from off to on) more then one gear can be overdriven
and our car is listed as a 4 speed with o/d.

*shrugs*