Friend borrowed vehicle and heater core hose leaked. overheated. DROVE it back, stopping to let it cool and adding water. The next day, checked coolant leveland oil level. Coolant most likely empty, oil level full. Changed out bad hose and replaced thermostat. Changed engine oil for good measure. Started vehicle and ran for a bit to make sure there were no leaks. Checked coolant level and it was low. Checked oil level and it was milky chocolate looking. What could have happened that caused coolant to leak in the oil after the repairs and there was no coolant in the oil i drained after overheating?