can someone please tell me the diffrence between the two D's in a ford taurus 99.?

D with the circle is Drive with "Overdrive". Without the circle, it's just regular drive. For normal driving & best gas mileage, use the circle'd D. If you're pulling a trailer or in a bunch of hills and it keeps downshifting, then use D without the circle.

I've had many taurus' and here's the thing. The 'D' with the circle around it is overdrive. That is 4 gears in your transmission. Primarily used for highway driving. The gas mileage will be much better if you use this gear on the higway. The 'D' without the circle is drive, 3 gears, and if you are doing over 55 miles per hour and let off the gas you will feel a lunge because its moving too fast for that gear and you need to be in overdrive (d with the circle around it). It is okay to go from d to overdrive as long as you let off the gas while driving. hope it helps.

Go here and download a manual:

http://www.motorcraftservice.com/vdirs/retail/defa...

I drive with DO (Overdrive) most of the time. There's one hill that I drive that I'll shift down to D due to the length of the hill and traffic. Other than that, DO is good.

The circle is supposed to be the letter "O" to indicate that gear as Overdrive.

D And D Ford

Check your manual, but one is probably over drive.