Preheat Engine Link

"PREHEAT ENGINE" refers to the process of warming an engine's internal components and fluids (oil and/or coolant) before starting it in cold weather, usually at or below 20°F (-7°C), to reduce wear and ensure a successful start.

For electric heaters, it is often suggested to run them for 1–5 hours, though some keep them on overnight, say. PREHEAT ENGINE

Common techniques include using electric block heaters, oil pan heaters, or forced hot air. "PREHEAT ENGINE" refers to the process of warming

In diesel vehicles, a pigtail-shaped light indicates that the are heating the cylinder heads before starting, usually lasting 30 seconds or less. usually at or below 20°F (-7°C)

Are you asking about a or an external heater (like a block heater)?