I bought my car from carmax about 3 months ago and i just want to make sure they put enough oil in. When looking at the dip stick its got a "min" and a "max" and right in between is the measuring bar. My oil with a semi cooled engine takes up 50% of the bar between min and max. Is this enough?

The oil (now 3,000 miles later) looks a little dark. I was thinking of putting in 8.5 qts of either 5w-40 or 0w-40 just to be safe. You just never know what's in your cars engine if somebody else does it.

Thanks in advance.