Q: Engine power dropped after over heating on 2005 Mazda Mazda6

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The car overheat after the roller of the adjuster got stuck. (He roller was lubricated with engine oil, replaced the belt and the engine temperature is normal. The engine power remain low to the extent that it take make some shudder noise before it moves. It is sluggish at low speed especially. The response is poor. I was told the cylinder head gasket is still good since the temperature dial read normal.
(1) Answer
I think the engine is damaged from overheating. Get a professional diagnosis so you know what you're dealing with.
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