While performing a cooling system pressure test on a medium-duty truck, the technician notices a steady drop in pressure without visible external leaks. The most likely cause is:

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Multiple choice — select the best answer

AFaulty radiator cap
BAir in the cooling system
CFailed water pump seal
DLeaking head gasket

✓ Correct answer: D. Leaking head gasket When a pressure test shows decreasing pressure without visible external leaks, a leaking head gasket allowing pressure to enter the combustion chamber is often the cause. This creates an internal leak not visible from outside the engine.

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While performing a cooling system pressure test on a medium-duty truck, the technician notices a steady drop in pressure without visible external leaks. The most likely cause is:

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