Messer
using 93 octane will not cause you oil to turn black quicker. Your car probably has high mileage on it. there fore lots of wear and tear on the internals of the engine. It is normal for oil to turn black that is what happens as the viscocity of the oil wears down. Just change your oil and oil filter. I personally use Mobil one synthetic. you probably want to use 10w30 in your car. But I know very little about anything but old chrysler products.