تنگی مسیر مایع خنک‌کننده

A coolant passage inside the engine restricted by sediment or corrosion. Unlike a blocked hose or radiator this cannot be inspected, which is what makes it the difficult version — the restriction is inside the casting.

The symptom is localised rather than general: one cylinder or one area runs hot while overall temperature looks acceptable, which promotes detonation the knock sensors genuinely hear. So knock codes on one bank with a normal gauge are worth taking here. Two coolant temperature sensors in different places disagreeing is the strongest available evidence, since it measures the flow problem directly. The cause is nearly always coolant history — water top-ups, mixed types, or coolant never changed — so the whole system is implicated rather than one passage.