Will a Bad Radiator Cap Cause Overheating?


Quick Answer

A defective radiator cap can cause an engine to overheat because the faulty part reduces the functional efficiency of the radiator. The coolant-system temperature is lowered in the radiator by passing through a series of fins and tubes, so anything that disrupts this process decreases cooling, which can lead to an increase in engine temperature.

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Will a Bad Radiator Cap Cause Overheating?
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Full Answer

When checking the radiator cap, make sure the sealing ring is undamaged. If it is a rubber ring, ensure it hasn't become brittle and cracked. The cap's pressure-relief valve can be tested by depressing it against its spring; effort to do this is required. The valve itself should move freely.

The owner can test the cap's efficiency by running the engine for a few minutes, then using a heavy cloth and a thick glove, can undo the cap to its first stop; never fully remove the cap as the pressurized hot water will erupt. If no escaping air or steam is present, the cap is likely defective and a new one needs to be fitted.

Ensure the new cap is rated correctly; the pressure rating is marked on it. This is important because the coolant system is pressurized, which increases water's boiling point. Fitting a cap with too low a pressure rating means decreased system pressure, which may again lead to overheating, while fitting one with too high a rating may lead to over-pressurization of the system.

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