Cooling Systems - PowerPoint PPT Presentation

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Cooling Systems Purpose Cooling system operation Principle components Purpose To remove surplus or unwanted heat generated by engine Bring cold engine up to normal operating temperature as quickly as possible Maintains proper engine operating temperature under all conditions Purpose

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Cooling Systems

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Cooling Systems

  • Purpose

  • Cooling system operation

  • Principle components

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  • To remove surplus or unwanted heat generated by engine

  • Bring cold engine up to normal operating temperature as quickly as possible

  • Maintains proper engine operating temperature under all conditions

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  • Liquid cooling systems allow:

    • A practical way to heat passenger compartment

    • Engine manufacturers to design more compact engines

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  • Water is circulated through engine by a centrifugal water pump

  • Water pump is driven off crankshaft by:

    • Accessory belt

    • Timing belt

  • Thermostat is closed while engine is cold and bypass allows circulation through engine only

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  • Once normal operating temperature is reached, thermostat opens and allows coolant circulation through radiator

  • Heat that is absorbed by coolant in engine, is transferred to radiator fins and dissipated to ambient air

  • Heated water is routed to heater core in passenger compartment to provide interior heat

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  • The thermostat is closed when the engine is cold, and the coolant flows through the bypass passage thereby bypassing the thermostat.

  • When the thermostat opens, most of the coolant flows through the thermostat to the radiator.

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  • Water pump

  • Thermostat

  • Bypass

  • Radiator

  • Heater core

  • Fan and fan clutch

  • Hoses and clamps

  • Auxiliary coolers

  • Pressure cap and overflow system

  • Anti-freeze

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  • As vehicle speed decreases, additional airflow is required to dissipate heat in cooling system

  • Additional airflow is provided by engine driven (rwd) or electric fans (fwd)

  • Engine driven fans use clutches to prevent fan operation at high engine speeds or low temperatures

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  • Hoses are necessary because engine is mounted on rubber mounts and designed to move during operation

  • Hose clamps are necessary to keep coolant from leaking out as well as keeping air from leaking into cooling system

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  • Auxiliary coolers are used to cool and preheat:

    • Engine oil

    • Automatic transmission fluid

  • Cooling system reaches normal operating temperature much faster than eng/trans lubrication systems

  • Cooling system is used to dissipate unwanted heat collected in eng/trans lubrication systems

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Air Conditioning Condenser

Oil Cooler



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  • Pressure caps are required to allow operating temperatures in excess of 212 deg. F

  • Pressurization increases boiling point 3 deg. for every 1 psi increase

  • Pressurization does not change temperature

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The operation of a typical pressure cap.


Asked Question

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  • Overflow system is designed to capture coolant as it expands when it is heated

  • As coolant cools and contracts, a pressure differential is created and coolant in overflow is forced back into radiator

  • System must be free of small leaks for proper operation

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When an engine overheats, often the coolant in the overflow container boils.



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  • Anti-freeze lowers freezing point of coolant

  • Water expands as it freezes and can crack or break the engine block and heads

  • 50/50 mix of anti-freeze and water drops freezing point to -35 deg. F

  • Anti-freeze can be mixed up to 70/30

  • Anti-freeze also contains chemicals and additives that inhibit rust and corrosion

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A radiator cap from a truck that operated with a low coolant level.



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When checking the cooling system, always inspect the coolant level in the radiator itself, but never when the engine is warm.

Always allow the engine to cool to room temperature before removing the radiator pressure cap.


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Mixing distilled water with antifreeze helps prevent problems such a lime deposits that could occur in the cooling system if regular tap water is used.


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Since the mid 1990s, many vehicle manufacturers have been using antifreeze coolant that is silicate and phosphate free.

Always check the owner’s manual for the specifications for the recommended engine coolant.


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