What issue is indicated by high exhaust gas temperatures in the engine?

High exhaust gas temperatures in an engine typically indicate a loss of turbine efficiency due to wear or degradation of engine components. As the engine components such as nozzles or blades wear over time, they may not perform as efficiently, leading to higher temperatures in the exhaust gases. This is because wear can lead to less effective combustion, causing more fuel to be burned without the requisite power generation, which ultimately reflects in elevated exhaust gas temperatures.

In contrast, excessive fuel supply would more likely lead to lower exhaust gas temperatures due to incomplete combustion. Proper engine performance would normally correlate with balanced exhaust gas temperatures that fall within the manufacturer's specified limits, and normal operational conditions would not typically result in high exhaust gas temperatures, but rather in stable and regulated readings. Therefore, high exhaust temperatures are indicative of an efficiency problem tied to the wear of turbine components, which aligns with the correct answer.