what causes sludge in the oil, and loud ticking noises. on 1997 Buick Century

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what causes sludge in the oil, and loud ticking noises after starting and gets worse the longer the engine runs. This started after getting an oil change at Firestone. Could it be the quality of oil they use? What can I do now? I hope it can be saved!
(1) Answer
What color is the sludge? if it's grayish white, pop the radiator cap while it's running (when it's cold, of course!) and look for bubbles, like blowing in a drink with a straw. If there's a pretty hardcore bubbling going on plus gray sludge, head gasket. If gray sludge and no bubbles, probably intake gaskets.
If it's regular old black sludge, run a can of engine flush and change the oil with a good Valvoline 10W40 or a 30 weight full synthetic.