Engine cooling systems

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Engine cooling systems

Ready for Review

►   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.
►   Coolant freeze point can be verified by a hydrometer or refractometer, both of which indicate the specific gravity of the fluid, revealing the ratio of anti-freeze to water.
►   Removing and reinstalling the heater core can be challenging; taking pictures as you go is highly recommended for ease of reassembly.

Source : http://www.cdxauto.com/cw/fundamentals/docs/24118_CH46_Ready%20for%20Review.doc

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