What operational conditions may lead to excessively high engine temperatures?

Operating at too much power with the mixture set too lean can lead to excessively high engine temperatures because a lean mixture means that there is not enough fuel being supplied to the engine relative to the amount of air. This makes the combustion process less efficient and results in a higher combustion temperature. The engine is working harder to produce the necessary power, and the excess heat generated cannot be dissipated effectively when the fuel is insufficient to cool the combustion chamber. This condition can cause significant stress on engine components and contribute to overheating, which could ultimately result in engine damage.

On the other hand, flight at low altitude with a heavy payload can increase engine load but does not inherently lead to excessive temperatures if the mixture is maintained properly. Frequent short flights might not allow the engine to reach optimal operating temperatures, and normal cruise operations are typically designed to keep engines within their safe temperature ranges. Thus, while these other situations may have various implications for engine performance, the specific combination of operating at high power and a lean mixture is particularly critical in causing high temperatures.