What Causes Engine Oil to Spray from the Radiator?
3 Answers
If engine oil is spraying from the radiator, it is recommended to replace the crankcase ventilation valve. Below are the reasons why engine oil may spray from the radiator: 1. Aging of the crankcase ventilation valve: Failure of components such as pistons, cylinder liners, piston pins, or piston rings can lead to loss of sealing effectiveness, resulting in oil spraying from the radiator. 2. Severe wear between the valve stem and valve guide: Excessive wear between the valve stem and valve guide creates too large a gap, causing oil to spray from the radiator. 3. Excessive exhaust gases in the engine: If the piston rings lose their sealing function, high-pressure gases from the cylinders can leak into the crankcase ventilation system, increasing pressure and forcing oil to spray out from the radiator.
I encountered this exact situation last time I drove - oil spraying into the coolant reservoir is no minor issue. It usually indicates engine oil has mixed with the cooling system. The most common causes are a blown cylinder head gasket or a faulty oil cooler, allowing the two fluids to cross-contaminate. In my case, I noticed oil streaks and smoke in the coolant reservoir, so I immediately pulled over and had it towed to the shop - turned out to be a blown gasket. If left untreated, the engine could overheat and seize, leading to catastrophic failure. Repairs become expensive and complicated, so I strongly recommend stopping immediately for inspection when this happens - never risk driving further.
Having worked on cars for many years, I've seen quite a few cases of radiators spraying engine oil, which is often caused by engine seal failures, such as a ruptured cylinder head gasket allowing oil and coolant to mix and spray out. In such situations, the vehicle's cooling efficiency drops significantly, making it highly prone to overheating, engine damage, or even fire. The safest course of action is to immediately turn off the engine and avoid restarting it, then check the coolant reservoir for any greasy residue or unusual odors. If confirmed, the faulty components must be replaced promptly. Delaying repairs can double the costs and potentially compromise driving safety.
