Also remember that an aircraft properly maintained has very tight maintenance schedules. As earlier posts mention, regular oil changes with 50 or 100 hour inspections, and top overhauls, full rebuilds (typically at 1000 and 2000 hours). So the concept of an aircraft engine that gets old and sloppy like a automobile rattletrap is just not supposed to happen.
Yes aircraft piston engines are air-cooled, but remember too that the typical flight profile of an aircraft engine is to start with a warm-up phase taxiing into position, take off at full power, then cruise at about 70% power or so steady for several hours until landing. It’s not stop-and-go like an auto, so the engine does not go through frequent changes in temperature during much of it’s operating life.