Cooling System Basics

Coolant flow, thermostat, radiator and fan.

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What you will learn

Trace the cooling circuit
Explain the thermostat
Diagnose overheating basics

Combustion produces far more heat than the engine can use, so coolant circulates through jackets in the block and head, carrying heat to the radiator where airflow releases it. The water pump provides flow and the thermostat controls how much coolant reaches the radiator.

Overheating has a small set of causes: low coolant, a failed fan, a stuck thermostat, a restricted radiator or a failed pump. Because overheating can warp the head, always tell the customer to stop rather than “drive it home”.

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Never open a hot cooling system — pressurised coolant can scald. Wait until it is cool and use the correct precautions.

Key points

Coolant flow plus airflow equals cooling.
Thermostat controls temperature; a stuck one causes overheating or slow warm-up.
Overheating can warp the head — act early.

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Key points

Coolant carries heat from engine to radiator
The thermostat controls temperature
Fan, airflow and pressure all matter

All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.