Engines: Engine Cooling

Cooling fundamentals	Cooling systems	The cooling system is designed to keep the engine operating at a given temperature and prevents the engine from seizing.
	Heat transfer	The internal combustion engine works by changing heat energy into kinetic energy. Heat can be transferred in three ways - conduction, convection and radiation.
	Vehicle coolant	Water can absorb more heat per volume than most other liquids, but it can allow corrosion and damaging electrolysis. This is controlled by inhibitors.

Cooling systems	Air cooling	Air cooling uses air to carry away heat. It works best on engines exposed to a high airflow. Cooling fins make exposed surface area as large as possible, allowing more heat to radiate away.
	Liquid cooling	A liquid cooling system uses coolant to remove excess heat from an engine. It also uses a heat-sensitive valve to control circulation to help an engine heat up and maintain its operating temperature.
	Rotary engine cooling system	Rotors in a rotary engine are cooled by oil from the lubricating system. Housings are water-cooled, with additives to protect its alloys. A pulley on the end of the eccentric shaft drives the water pump and fan.

Cooling system components	Basic cooling system components	The primary components in a vehicle cooling system are: radiator, thermostat & housing, water pump, cooling fan, radiator hoses and heater hoses.
	Radiator	Many radiators are mounted at the front of the vehicle in the path of greatest airflow. The air carries heat away, cooling the liquid before it returns to absorb more heat from the engine.
	Coolant hoses	Cooling system hoses are flexible to allow for movement, and molded to fit the shape needed. Most hoses are made of rubber, and reinforced with a layer of fabric.
	Water pump	The water pump pumps coolant through the engine and radiator. It is belt-driven from a pulley. A hose connects it to the bottom of the radiator.
	Cooling system thermostat	A thermostat shortens an engine's warming-up period. It is a valve operated by coolant temperature. It stops coolant circulating through the system while the engine is cold.
	Cooling fans	A fan helps generate airflow through a radiator. It can be driven either by a belt off the crankshaft, or electrically. It can be controlled according to temperature.
	Temperature indicators	A temperature indicator is a device that is sensitive to engine temperature. It sends readings to a temperature gauge or a warning lamp.
	Radiator pressure cap	One way to help prevent a coolant boiling is to use a radiator pressure cap that uses pressure to change the temperature at which water boils.
	Recovery system	A recovery system keeps the cooling system full. As engine temperature rises, coolant expands and flows out into a container. As it cools it returns to the radiator.
	Boiling point & pressure	Changes in water pressure can change the temperature at which it boils.
	Electrolysis	Electrolysis is a chemical and electrical process. It occurs when two different metals are in contact, in the presence of a moist agent such as water. One of the metals is corroded away.
	Centrifugal force	Centrifugal force is a force pulling outward on a rotating body.
	Thermo-switch	A thermo-switch opens and closes according to pre-set temperature levels.

Cooling system procedures	Checking & adjusting coolant	The objective of this procedure is to show you how to check and adjust coolant levels and test coolant quality in a vehicle with a recovery reservoir. There are two correct level marks on the reservoir because the coolant in the system expands and contracts in volume depending on how hot it is.
	Draining & refilling coolant	The objective of this procedure is to show you how to drain cooling system and refill with correct mixture of engine coolant. Some vehicles have drain plugs on the side of the engine block. The shop service manual will tell you if these need to be opened when draining the coolant.
	Checking & replacing a coolant hose	The objective of this procedure is to show you how to check, remove and replace coolant hoses. Never try to assess the serviceability of a coolant hose while the engine is hot.
	Testing cooling system pressure	To test the cooling system for both internal and external leaks, a pressure tester is normally used. These are often referred to as cooling system testers or analyzers. The objective of this procedure is to show you how to test a cooling system to confirm that it is without leaks and has the ability to hold the pressure specified by the manufacturer.
	Removing & replacing a radiator	The objective of this procedure is to show you how to safely remove and replace a radiator. Once the radiator has been removes carry out a visual inspection of the radiator to ensure that it is suitable for reinstallation in the vehicle.
	Removing & replacing a thermostat	The objective of this procedure is to show you how to safely remove and replace a cooling system thermostat. Coolant in the cooling system could be above its boiling point. Never open a radiator cap fully until ALL pressure has been released.
	Inspecting & adjusting an engine drive belt	There are two types of drive belts: V-type and Serpentine type. The objective of this procedure is to show you how to inspect and manually adjust engine accessory drive belts.
	Replacing an engine drive belt	Many vehicles require the technician to manually adjust the tension on the belt. Other vehicles have an automatic spring tensioning system. Depending on the system used on the particular vehicle, you should always follow the manufacturer's service instructions. The objective of this procedure is to show you how to remove and replace an engine accessory drive belt.

Topic group	Topic	Summary