Which device indicates when exhaust temperatures are abnormal?

Answer: C — Pyrometer warning light

The pyrometer warning light is designed specifically to measure and indicate the temperature of the exhaust gases within an engine. When exhaust temperatures exceed normal operating levels, the pyrometer warns the driver through a dashboard light or alert system. This is crucial because elevated exhaust temperatures can indicate potential issues such as engine overload, failing components, or improper air-fuel mixture, leading to engine damage if not addressed promptly. The other devices mentioned do not serve this specific purpose. The oil pressure gauge monitors the oil pressure in the engine, ensuring that the proper lubrication is present, while the fuel gauge tracks the amount of fuel in the tank. The temperature control system is more associated with regulating engine coolant temperatures rather than exhaust temperatures. Therefore, the pyrometer warning light is the device that directly indicates when exhaust temperatures are abnormal.