Why is there oil in the motorcycle air filter?
2 Answers
If the motorcycle air filter is a sponge foam filter element, it is normal to have a small amount of engine oil on it. Here is some relevant information about motorcycle air filters: 1. The significance of the air filter: Air passes through the filter and enters the cylinder through the intake valve (throttle), enabling the gasoline to burn. The intake valve opens and closes in synchronization with the piston movement. Therefore, the oil in the filter is the engine oil ejected through the intake valve during piston movement. 2. Excessive oil is abnormal: If there is too much oil, it may be because the motorcycle has been tipped over, causing the engine oil to flow back into the air filter through the breather tube. Additionally, check if there is too much oil in the engine, if the cylinder gasket is damaged, or if pressure is blowing oil from the engine breather tube into the air filter. For scooters, some cylinder head covers may have issues that can also cause similar situations.
I've been riding motorcycles for ten years, and it's quite common for the air filter to get oily, mainly due to oil vapor backflow. When the engine is running, the high pressure in the crankcase causes oil mist to travel through the ventilation tube and accumulate in the air filter. It could also be caused by overfilling the oil or aging seals failing. If you notice this, clean the oil stains from the air filter promptly; otherwise, dust sticking to it can clog the intake, leading to reduced engine RPM, increased fuel consumption, and even cylinder scoring if left unchecked for long. I encountered this issue after my last long-distance trip, and a simple fix restored normal operation. I recommend regularly checking that the oil level doesn’t exceed the maximum mark and maintaining the vehicle’s ventilation system to prevent abnormal pressure buildup.
