What's the difference between having it gear D4 than D3?

Question

My car is automatic just wondering when exactly you should have it on D3 or D4? Also theres a just a 2 at the bottem. . I know the are they have to do with switching gears but when should you drive on D3 compared to D4? Does it save you gas?

Answer 1

Just keep it in D4. Many cars with 4 speed automatics don't even show D4, just 1 - 2  and D.

D3 would be when you need a bit more power, maybe going up a hill, and it'd downshifting and upshifting too much. Sometimes it can't decide which gear it wants to stay in.

You'd also put it in D3 (or even 2) on a big downhill to let your engine help brake of slow you down, instead of riding the brakes.

Drive safe.

Answer 2

D4 is what you want to use most of the time.  That will have the transmission shifting into the highest gear (4th) when the speed and engine load are correct for it, causing the engine rpms to be at their lowest for the speed, and saving you gas.  D3 would be used only when you want to make it easier for the engine to pull, as when climbing a mountain, of pulling a trailer uphill.  But, mostly, use D4.