Intercooler (Charge Air Cooler)

Air-to-air intercoolers sit in the airflow at the front of the car; air-to-water types use a coolant circuit. Cooler air lowers knock risk and increases power. Intercooler efficiency drops if the fins are blocked by dirt or insects, so the charge air stays hotter.

Compressing air heats it. The intercooler passes the hot air through thin tubes and fins, where it gives off heat.

Oil in the intercooler can point to turbo seal wear. Split hoses or leaks reduce boost and power. The intercooler and its hoses are checked for leaks with a pressure test when boost-related codes appear.