What best describes glow plugs?

• A. They generate sparks to ignite fuel
• B. They regulate fuel injection timing
• C. They are small electric heaters that heat the combustion space and switch off automatically
• D. They measure cylinder temperature

Answer: (C)

Glow plugs are small electric heaters placed in the cylinder head to preheat the combustion space, making ignition easier in cold conditions. They work by heating a element until the surrounding air-fuel mix becomes hot enough to ignite when the engine cranks. The electrical circuit is designed to switch off automatically once the engine starts or the preheat cycle reaches the required temperature, preventing overheating and draining the battery. They don’t provide a spark to ignite fuel, they don’t control when fuel is injected, and they aren’t used to measure cylinder temperature, which is why this description best fits their function.