I just recently inspected the spark plugs in my 2016 Jeep Patriot with 2.4 liter 4 cylinder engine. All 4 plugs had a brown, tan tint and looked good with no signs of plug fouling. Even the center electrode had very little wear and was not rounded. I cleaned the plug tips with sandpaper, set proper gap and reinstalled with anti-seize compound on the threads. I did this more as a curiosity satisfaction and not because there was an engine performance issue or diagnostic code set.The engine has crossed the 60,000 mile mark. The owner's manual recommends replacement at 30,000 mile intervals. And Chrysler tends to follow the 30,000 mile replacement interval for spark plugs on many of its engines. In this particular instance I see no reason to replace the spark plugs and plan on continuing to use them to at least the 100,000 mile mark. Why does the manufacturer seem to set a rather arbitrary and low mileage interval for spark plug replacement?