What Causes Engine Oil to Leak into the Radiator?
2 Answers
Causes of engine oil in the car radiator: 1. Blown head gasket: After the head gasket is damaged, the oil passage and coolant passage become connected. Since the oil pressure is higher than the coolant pressure, the oil enters the coolant passage and then the radiator. Observe air bubbles escaping from the surface of the radiator coolant. After stopping the engine, the coolant will flow into the oil passage and then into the oil pan. 2. Cracked cylinder liner: Due to the high fuel pressure in the cylinder, oil and diesel are "squeezed" into the coolant through cracks in the cylinder liner under high pressure. Observe the surface of the coolant for intense movement of air bubbles. 3. Faulty oil cooler: During assembly or manufacturing of the oil cooler, cracks in the cooling tubes, poor welding, or freezing and cracking of the cooling tubes due to not draining the coolant properly in winter can cause oil to enter the coolant. If you observe the surface of the radiator coolant, it is generally calm.
As a long-time auto mechanic, I've found that the primary cause of engine oil leaking into the radiator is a blown head gasket. This gasket sits between the engine block and cylinder head, designed to seal oil passages from coolant channels. When it deteriorates from age or cracks due to excessive heat/pressure, oil seeps into the cooling system. Another common culprit is cracks in the engine block or cylinder head itself, typically caused by overheating or metal fatigue from improper use. The telltale signs include brownish, milky coolant with reduced cooling efficiency, accompanied by engine overheating or white smoke while driving. Left untreated, this can lead to hydro-lock or catastrophic engine failure. I recommend owners regularly inspect coolant color and seek immediate repair if contamination appears - delaying could mean costly engine rebuilds.
