I rent a lot of cars. Lately I have been checking the oil when I fill the car. I have noticed that some cars (usually with 7k-15k total miles) the oils look quite dirty and dark with even at little as 2k-3k miles on the oil. As constrasted with my 95 6 cyl Camry at 3k with Mobil1 and Pureone filter, the oil is usaully just a very dark amber. Also, I just put a new reman Nissan V30 engine in my 1987 Pathfinder. With 1600 miles the Mobil 1 oil/Pureoone is just a light amber. Is this something with newer cars or just the cheaper oils and filters of rent cars? In other words, is Mobil 1/Pureone that good or it is some combo of cheaper oils/filter, hotter running cars, or rent car drivng patterns? BTW, the Hertz cars usually have oil change sticker around 5.5K intervals.