Usually the cam breaks due to it getting seized in the head. (unless someone dropped the cam or ? before installation)
You may want to check your oil galleys in the head and then the cam journals for scoring. If there looks like silver oil draining from them, metal particles could have contaminated your oiling system..
What did you do to fix the overheating problem?
What was causing it?
It could have degraded the oil and then, with the turbo cooking it further.. You may want to pull the pan just for a closer examination. Coolant is only about 60% of the total engine cooling. The oil usually does the rest.
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