If a vehicle is overheating, the diagnostic process has become more complicated in modern cooling systems. Part of the reason is cooling systems have become more integrated with the engine management and emissions reduction systems. Old cooling systems reacted to heat generated by the engine. New systems anticipate and influence changes in coolant temperature.
To gain control over coolant temperature, OEMs have introduced several new cooling system components that can control the flow and temperature of the coolant. These include grille shutters, electronic thermostats, flow control valves and electric water pumps.
To diagnose an overheating or overcooling complaint, the most important thing is to understand what happens when a component fails and how the control system reacts.