Why is heated liquid coolant pumped through the upper inlet of the radiator instead of the lower inlet?

The correct reasoning for why heated liquid coolant is pumped through the upper inlet of the radiator is that it facilitates more efficient cooling by promoting an even distribution of heat transfer throughout the radiator. When the hot coolant enters from the upper inlet, it pushes the cooler liquid through the radiator, allowing for optimal heat exchange as air flows over the cooling fins.

This method ensures that the coolant, which has absorbed heat from the engine, spreads that heat out evenly as it circulates through the radiator. By entering from the top, the coolant can then flow downwards, cooling as it travels through the radiator's core. This effective cooling process is crucial for maintaining the engine's optimal operating temperature.

While collecting cooler liquid at the bottom plays a role in the circulation and efficiency of the cooling system, it is not the primary reason for the design choice of the upper inlet. The focus is more on maximizing the radiator’s cooling efficiency and ensuring even distribution of coolant flow to enhance heat dissipation.