What condition would cause an engine to run above normal operating temperatures?

An engine running above normal operating temperatures is primarily influenced by the cooling system's ability to regulate temperature effectively. A malfunctioning thermostat can prevent the coolant from circulating properly, leading to overheating. Additionally, having an oversized radiator creates no real benefit; while it can increase coolant capacity, it may not ensure efficient temperature regulation and could also be responsible for poor engine temperature management if it doesn't work harmoniously with the rest of the cooling system.

However, low oil levels can also contribute to increased friction and heat generation within the engine, and a dirty fuel filter can affect engine performance, which may indirectly impact the engine’s temperature. Neither of these conditions directly leads to overheating in the same manner as a faulty thermostat. Therefore, the correct answer emphasizes the significance of the thermostat's functionality in maintaining optimal engine temperatures, highlighting how a malfunction can cause the engine to run hotter than it should.