Why does coolant enter the lowest portion of the water jacket and push up?

The primary reason coolant enters the lowest portion of the water jacket and pushes up is to ensure that the coolant is always in contact with all components of the system. This design allows for effective heat absorption from the engine block or other heat-generating parts. By entering from the bottom, the coolant can uniformly rise and circulate through the entire system, removing heat as it travels. This is crucial because it maintains optimal operating temperatures, prevents overheating, and ensures that every part of the engine or component gains the necessary cooling.

Maintaining consistent contact with all components also helps in achieving balanced temperature distribution throughout the system. If the coolant were to enter from higher positions, it could lead to areas not being adequately cooled, potentially causing hotspots and reducing the overall efficiency of thermal management within the system.