A Look at What Crankcase Pressure Can Tell Us on a Turbo Subaru Engine

If you have been closely following the videos that I made that take a look at Catch Cans, Air Oil Separators, and AOS routing, etc., almost 2 years ago, I started using a fitting on an oil cap to monitor crankcase pressure. At the same time, I had a conversation with Harvey at The Boostcreep about what I was trying to take a look at, and he was curious too. So I made him another oil cap with a vacuum fitting, and for a little over a year, he has been able to log crankcase pressure on the majority of the cars that he has tuned. In that time, he has recorded some really good data, and we have had some really good conversations about things that we both have discovered by being able to see what is happening with crankcase pressure.

I was able to meet up with Harvey at his dyno recently so that we could take a look back at 4 different cars that he had logged. Each one of these logs gives some valuable information about crankcase pressure and the factory PCV system.

Case 1 is a 2019 STI that is completely stock with 1,200 miles on the engine - 6:50

Case 2 is a Forester XT that starts out with an issue in its PCV system - 15:14

Case 3 is an interesting comparison of 2 different Air Oil Separators on the same car - 22:42

Case 4 is a car that had an issue on the dyno where crankcase pressure was a key to diagnose what happened - 28:05

This video ended up being the longest one we have put up to date, but since each conversation is directly connected to the next and the conclusions that we come to are all built upon these examples, I decided to put the video up in its entirety. So thank you very much for watching, and hopefully you get something helpful out of this video.