The phenomenon you are describing is often observed when starting a cold engine, and it is related to the engine's coolant system. Here's how it typically works:
Engine Warm-Up: When a vehicle has been sitting for a while, the engine cools down, and the coolant temperature drops. The coolant is responsible for absorbing and carrying away the heat generated by the engine.
Coolant Circulation: Before starting the engine, the coolant pump is inactive, and the coolant is not circulating through the engine. As a result, the heat generated by the engine during the previous operation is retained within the engine and its surrounding components.
Heat Dissipation: When you attempt to start the engine, the starter motor engages, and the engine cranks. During this process, the engine's cylinders and components begin to move, causing friction. This friction generates some heat in the engine, which contributes to the initial heat you feel coming from the engine.
Heat Exhaust: Additionally, the heat you feel may also come from the exhaust system. The exhaust manifold and pipes retain residual heat from the previous engine operation, and when the engine is cranked, this heat is emitted through the exhaust system.
Once the engine starts, the coolant pump begins to circulate the coolant, and the engine warms up gradually. As the coolant absorbs the heat generated by combustion, the engine temperature rises, and the initial heat you observed before starting the engine diminishes. This process allows the engine to reach its optimal operating temperature, ensuring efficient performance and reduced wear on engine components.