Blowing white smoke out your exhaust? 996/Boxster
Most people’s initial reaction when they see white smoke coming out of their exhaust, is to assume the worse…..blown headgasket, slipped cylinder lining, catastrophic engine failure. While on rare occasion that is the case, many times it is nothing more than a bad Oil Air Separator (OAS, AOS, Air Oil Separator, etc).
996, 997’s, and Boxsters use an oil air separator which basically reduces oil vapor that recirculates in the engine. Unfortunately, they use a rubber diaphragm that is prone to failure. The result is excessive smoke out of the exhaust on start up and driving. Some smoke on start up is normal on a horizontal engine, but it shouldn’t last more than 10-15 seconds. When the OAS fails, the car will start smoking for longer periods of time, until is a huge smoke cloud as you drive. One of the other symptoms of a failed OAS, is a chirping or harmonic noise near the rear of the engine by the transaxle. The noise is due to the air passing through a small tear in the diaphragm. Once the OAS completely fails, the noise will probably not be audible as the air is passing through a large tear, and not a small one.
Fortunately the part is cheap at less than $150, and a couple hours to replace.
I cut open a recently failed OAS that was starting to not only make noise, but also cause some light smoke issues.
You can see the main tear in the middle (red arrow). There was also another tear about the same size near the perimeter on the other side which is hard to see.