Because of blown head gasket. Heads and gasket appear ok with no apparent damage to gasket or warpage to head. I will take the Calipers to the head studs to see if they elongated. The unfastening torque felt very different bolt to bolt so they might have been stretched out just enough to cause a leak. They are ARP but the very base level I'm assuming... I checked the receipt from EPR and they are like 100 bucks for the set.. I think ARP2000 run for 300.. Will Make sure these gets used this next build.