replaced water pump, flushed coolant system, new coolant. coolant level will stay up and then drop for no reason. mechanic tested coolant, head gasket. nothing found. now water or coolant in oil.
2001gmc 5.3 engine with 130000 mile antifreeze leak on 2001 GMC Sierra 1500
if there is coolant in the oil you either have intake or head gasket problem or possible cracked block