The radiator cap seals the top of the radiator (or coolant reservoir on some systems) and maintains correct system pressure, which raises the boiling point of coolant.
If you notice any of the following, the part likely needs replacement:
Coolant loss with no visible external leak
Overheating from insufficient system pressure
Coolant bubbling or spraying out when the cap is opened (when hot — never open when hot)
Installation information
Screws or clips onto the radiator or reservoir neck — always check the sealing gasket is intact before fitting.
Frequently asked questions
The cap maintains system pressure, which raises coolant’s boiling point above 100°C — a cap that can’t hold this pressure lets coolant boil at a lower temperature, reducing cooling efficiency.
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August 2026
★★★★★
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Toyota Avensis
August 2026
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June 2026
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May 2026
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