What Causes Oil Spray from the Exhaust Pipe?
3 Answers
It is normal for a diesel engine's exhaust pipe to have slight oil spray or a small amount of oil at the outlet. However, severe oil dripping from the exhaust pipe is abnormal. The exhaust pipe is usually connected to the crankcase or valve cover. Possible reasons include: 1. The crankcase ventilation valve is aging, or there is a malfunction in the piston, cylinder liner, piston pin, or piston rings, leading to a loss of sealing effect and causing oil spray. 2. Severe wear between the valve stem and valve guide creates excessive clearance, resulting in oil leakage downward. 3. The design itself has defects, leading to oil spray from the exhaust pipe.
Old driver here, I've been driving trucks for twenty years, and oil spraying from the exhaust pipe is a common issue. It's mainly due to worn piston rings or cylinder liners, which compromise the seal and allow oil to seep upwards; or aging valve guides and seals, letting oil leak in from the valve stems. Another possibility is a clogged crankcase ventilation valve, where excessive exhaust pressure forces oil out. The last time I encountered this, it was due to a leaking turbocharger bearing mixing oil into the exhaust pipe—upon disassembly, the oil seal was cracked. Ignoring this problem leads to more oil being sprayed out, eventually ruining the catalytic converter, and severe oil burning may necessitate an engine overhaul. I recommend checking cylinder compression and valve seals early on. Replacing the ventilation valve, which costs just a few dozen bucks, can solve most issues.
Recently helped a friend fix his old Tiguan, which was spewing engine oil from the breather pipe like a mist. The principle is actually quite simple: when the internal exhaust gas pressure in the engine is too high, the oil vapor that should have been recycled through the PCV valve is forcibly blown out through the breather pipe. Common causes include excessive piston ring wear leading to a surge in crankcase pressure, a leaking turbocharger oil seal allowing oil to mix directly into the exhaust pipe, or the use of low-quality engine oil causing sludge to clog the ventilation system. Upon disassembly, I found that the valve cover gasket had deformed, leading to seal failure. Replacing the gasket and adding a bottle of sludge cleaner solved the problem immediately. If oil spewing is detected, it must be addressed promptly; otherwise, engine carbon deposits can double, and fuel consumption can skyrocket in no time.
