What Causes a Hissing Sound in the Engine Compartment at Idle?

1 Answers
Felicity
07/30/25 9:00am
Engine compartment at idle when there is a hissing sound for the following reasons: Valve seat wear: The working surface of the valve and valve seat is worn or eroded, producing spots, pits, or carbon deposits. Poor valve sealing: Excessive clearance between the valve stem and valve guide causes the valve stem to wobble, preventing the valve from sealing properly. Alternatively, a bent valve stem or misaligned valve head can also lead to poor sealing, resulting in a "whooshing" or "hissing" sound. Weak spring tension: Reduced or lost elasticity of the valve spring, or a broken spring, can cause improper sealing between the valve and valve seat. Insufficient valve clearance: When the valve stem expands due to heat, the tappet or rocker arm may push the valve open, preventing it from fully closing and causing a hissing sound.
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