Oil is responsible for two things. One, providing lubrication to your engine to prevent damage to the cylinders and two, it has an additional cooling property. Regular oil changes, at the factories specified intervals, with prolong the life of your engine. Over time and mileage, the lubrication and cooling properties of your oil will break down, making the engine oil appear dirty and thin. The engine oil can also indicate the health of your engine by examining the color, how quickly the engine discolors the oil and the contaminants that are in the oil, such as metal shavings. On the topic of contaminants, the oil filter is also very important to ensure none of the contaminants clog the channels the oil flows through, preventing proper oil circulation. All repairs are priced as such; Price of part, plus installation fee, plus fluid recycling, plus trip charge.