This calculator is designed to supply the area of any potential collection surface of any length and width in square feet and/or square inches, based on the length and width values entered in feet and inches, and the potential and estimated actual rainwater recovery in gallons.
It depends! Read the owner's manual for the brand of car you own or want to drive as each auto maker determines when to change the oil. Generally, I've read and experienced that full synthetic oil can last up to 5K-7500 miles, but... it also depends on other factors such as your driving style and where you live. VW has listed in its newer cars, like the 2015 VW Golf, that oil changes can be done in 10k miles!
Oil changes are needed frequently to avoid this problem (ergo every 3,000 to 5,000 miles). The durability of synthetic oil at the same engine temperature makes it a better-performing product because synthetic still stays in liquid, usable form longer. This tolerance for temperature means the oil can stay in the engine and can last as much as 7,000 miles before changing. Most oil and car warranties will put the maximum length of mileage before a change at 7,500 for petroleum-based products (many cars are closer to 5,000 even with today's better engines). Given the heat-tolerance properties of synthetic oil, 7,500 miles is not an issue.