In a turbocharged or supercharged engine, heat is produced when induction air/charge air is compressed, and the engine is under boost pressure. This heat robs the engine of power and torque by reducing the charge air’s density and increasing the engine’s combustion temperatures and octane needs. In a best-case scenario, hot air causes reduced engine efficiency with measurable losses in horsepower and torque. In a worst-case scenario, engine misfires, pinging, knocking, and engine damage are possible
Vehicle manufacturers often use a dedicated coolant circuit to help cool this induction air, called charge air coolers (CAC). CAC can use liquid coolant, much like your engine, to transfer heat out of and away from the induction air.
Air pockets within the liquid coolant circuit greatly reduce the CAC efficiency. Air trapped within the intercooler or heat exchangers limit the amount of heat transfer able to occur, effectively rendering the system smaller. Air that gets trapped in or near the pump and lines can cause cavitation. Cavitation can completely slow or stop coolant flow through the system and in some cases cause the pump to completely shut down and turn itself off in a self-protection mode. Regardless of location, air in the system is not desired and detrimental.
Air can get trapped and remain in the system for a variety of reasons:
Poorly performed initial fill from the manufacturer (Widespread and common)
Poorly designed coolant flow paths creating high spots and traps for air pockets that are not able to be released through normal pump flow and operation, even with reservoir
System opened or serviced for repair or upgrades
Insufficient and poorly designed service tools and methods to fully bleed air