How does the air get trapped inside the engine?

Many newer model vehicle designs have lower hood lines and are more aerodynamic, which means that the engine is positioned higher than the radiator. While this promotes a more attractive, sleeker look, it creates a problem within the radiator.

Basic physics tells us that water, which is part of the engine coolant, seeks a natural level. The coolant cannot be drawn into the engine efficiently because air exists between the upper portion of the engine block and cylinder head(s).