I am currently driving a 99 Jeep Wrangler 2.5L 4cyl. My engine only takes 4 quarts and I have been running mobil 1 with a k&n filter, mobil 1, or Napa Gold (which even one I have at the time) filter and was wondering if I should change my oil more than the every 4-5k that I have been since I only have 4 quarts circulating through my engine. Would less oil mean that it will get dirtier that lets say a Jeep with the 4.0 engine and 6 quarts of oil in it?