► Most cooling systems rely on coolant, a special mix of chemicals (anti-freeze) and water

► Coolant absorbs heat from the engine, is cooled in the radiator, and flows back to the engine to absorb more heat.

► Heat travels in one of three ways: conduction, convection, or radiation.

► Coolant works to keep an engine from overheating and from freezing.

► Coolant must contain anti-freeze to prevent the water content from freezing and to reduce corrosion.

► Anti-freeze contains either ethylene glycol (toxic) or propylene glycol (nontoxic).

► The combination of water and anti-freeze lowers the freezing point and raises the boiling point of both components.

► Manufacturers can create more efficient combustion by raising the engine’s operating temperature, creating more pressure, and causing coolant to boil at a higher temperature.

► Radiator caps maintain a specified pressure throughout the cooling system, generally 13–17 psi (89.6–117.2 kPa).

► Changing coolant regularly prevents acid buildup and electrolysis.

► The stationary parts of the cooling system (heater core and radiator) are connected to the engine via radiator and cooling hoses.

► Modern vehicles have replaced the thermo-siphon process for moving coolant through the engine with a water pump that forces coolant through the system.

► An engine thermostat regulates coolant circulation, keeping it in the engine until the engine reaches operating temperature.

► Engineers have developed a reverse-flow cooling system in which coolant is first pushed through the cylinder head, thereby better equalizing temperature between the block and head, which extends the life of the head gasket.

► Engines with the reverse-flow cooling system must have a surge tank to capture steam and reconvert it to coolant.

► Rotary engines use similar cooling systems to piston engines, with a radiator, thermostat, radiator hoses, and water jackets.

► The radiator’s function is to allow coolant to pass through it and to conduct heat away from the engine.

► Cooling tubes in the radiator core run in a vertical (down-flow) or horizontal (cross-flow) design.

► Radiator pressure caps contain a spring-loaded valve to allow excess coolant to pass into the overflow container, and a vacuum valve to allow coolant to be pulled from the overflow container back into the radiator when it is needed.

► A surge tank is situated as the highest component so that it collects any air present in the system and allows for easy air removal.

► In a recovery system, coolant flows into an overflow container and then back into the radiator so that no coolant is lost.

► The thermostat’s valve is controlled by a wax pellet that melts and expands and forces the valve open against spring pressure.

► Thermostats installed on the inlet side of the engine better control the amount of cold water flowing into the engine.

► The water pump uses centrifugal force to drive coolant into the water jackets.

► A fan clutch is driven by an accessory belt and uses a viscous fluid to control speed changes of the fan, determined by air temperature from the radiator.

► A solenoid-controlled fan clutch replaces the bimetallic spring with an electric solenoid controlled by the power train control module.

► Radiator hoses must be correctly clamped to the radiator assembly or a leak will develop.

► Some heater hoses contain a coolant control valve to regulate coolant flow when the air conditioner is turned on.

► The three types of drive belts for the water pump are V-belts, serpentine belts, and toothed belts.

► To ensure minimal slippage, drive belts are tightened around the pulley by tensioners.

► Either a temperature gauge or a temperature light can function as a coolant temperature indicator.

► Coolant passages are critical to the transfer of heat energy so coolant must be serviced regularly to prevent the passages from becoming clogged.

► The heater box contains air doors and actuators that work to control passenger compartment airflow.

► IAT coolant is the standard green coolant used in many vehicles and must be changed every 2 years or 24,000 miles (39,000 km).

► OAT coolant is an extended-life coolant that should be changed every 5 years or 150,000 miles (241,000 km).

► HOAT coolant (yellow) combines inorganic and organic additives and is also an extended-life coolant.

► POAT coolant, the newest type, is a very long-life coolant that should be changed every 7 years or 250,000 miles (402,000 km).

► Cooling systems need regular maintenance to ensure engine longevity.

► Common cooling system diagnostic concerns include coolant leaks, thermostat that is stuck closed or open, faulty water pump, inoperative cooling fan, or failed head gasket.

► Test pH concentration of the coolant to ensure the anti-freeze acid inhibitors are working correctly.

► Measure the voltage of the coolant to determine if electrolysis is occurring due to acidic coolant or faulty grounds.

► Always follow EPA regulations for handling and disposing of coolant.

► Coolant condition and level should be checked regularly; coolant should be at the correct level mark (upper or lower) according to engine temperature.

► When removing and replacing a radiator, be sure to properly catch, handle, and dispose of or replace the coolant.

► Do not attempt to remove or replace the thermostat until the engine has cooled for at least 30 minutes.

► Potential engine drive belt problems can be belts that are cracked, oil soaked, glazed, torn, or bottomed out.