oil in air filter

This is on some vehicles that have oil vapor recuperation, this is to stop oil vapor and crankcase pressure build up The oil mist goes into the airfilter and is breathed in by the motor. It is one of the more stupid sides of automotive engineering, as that oil mist could be sucked in on the other side of the filter, the oil will build up in the filter, slowly reducing the air filters capacity to pass air as easily as possible. The upshoot of a partially blocked filter is that the engine is now not recieving enough air for its air/fuel ratio, so the engine runs richer. Less power. Less fuel efficiency. Bad emissions. The reason that they let this vapor into the filter is so that it is caught by the filter, and not burned off. Because if you have oil vapor in your combustion, you make more bad emissions. So it is going to cost you an air filter more often than it should. In the old days, this oil vapor was vented to the atmosphere. Bad bad bad. How much oil is getting into your air filter? If it is a lot, then you may have piston blow-by, which is generating more hot gasses in the crankcase than is useful, older engines suffer from. A rule of thumb that I use, is that if the oil spread in an air filter approaches a quarter of the surface of the airfilter, I change the air filter. It is a good idea to consider that the air filter should be changed every single service, some people ignore this advice.