Coolant Mixing With Engine Oil reason The mixing of coolant with engine oil can occur due to a number of reasons, including: Blown Head Gasket: A blown head gasket can allow coolant to leak into the oil passages, resulting in the mixing of coolant with engine oil. This can cause damage to the engine if left untreated. Cracked Engine Block: A cracked engine block can also allow coolant to enter the oil passages, resulting in coolant mixing with engine oil. Damaged Cylinder Head: A damaged cylinde