Oil in my 2012 Sonata 2.4L is black on the dip stick in 2000 to 3000 miles. Dealer says normal for this car, I don't believe it. What do others see? Also only gets about 32 mpg on highway and has black deposits on the tailpipe. I have gotten better than rated mileage on every other car I have owned so I don't believe it is my driving technique. Any thoughts?