Mechanic question. My new mechanic (I had just assumed all mechanics knew what oil to put into what car) changed the oil from 0-20 synthetic, to 15-40 mineral. 5000 km ago. It was just changed again, to 15-40. I was under the hood checking for a coolant leak, and the valves were really loud. I could hear them well, as opposed to their former silence. Is it too late to ask him to change back to the 0-20? Or is this just a function of an aging car. 2017 Fit, with 85,000 km in very hot weather year round. Thanks