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 3 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; 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	Water can absorb more heat per volume than most other liquids, but it can allow corrosion and damaging electrolysis. This is controlled by inhibitors.
	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 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 also a method of epilation. In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them.
	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	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	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	You may need to use a torch to inspect the coolant hoses so that you can clearly see if the surface is starting to crack.
	Testing cooling system pressure	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	If changing coolant, dispose of the old coolant properly in accordance with environmental and legislative requirements.
	Removing & replacing a 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	A belt that has been soaked in oil will not grip properly on the pulleys and will slip. If the oil contamination is severe enough for this to happen, replace the belt.
	Replacing an engine drive belt	If you don't have a tension gauge, you can estimate the tension by pushing the belt inwards with your hand.