i had this same [similar] after i changed my water pump! Make ABSOLUTELY sure the radiator drain plug is fastened tightly! These were warning signs that my plug was inching its way out and leading up to the whole thing falling out and my coolant dumping out into the middle of the road; leaving me stranded and looking like an asshole.
Also, if you spilled coolant onto your engine at all, it could be the liquid burning when it touches the engine block.
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