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GU713 MP8 head issues

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So I have 2 trucks so far at around 250k+ miles started to misfire. 2016 Mack Granite GU713 with the MP8.  Both start loosing coolant internally. 

Computer diag showed mechanical failure in the turbo, and one had cly 5 misfire, and the other was cly 6. Upon removing the heads we found the heads to be cracked, and chip missing off of a exhaust valve on both heads, which traveled to the turbo and jammed them up. 

The egg coolers are not leaking. No coolant in the oil. It seems the heads crack allowing coolant to hit the valve and causing it to crack. 

Has anyone seen anything like this. I'm worried this is working through my fleet. 

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