The constant pressure valve (CPV) on the S54 engine comes from the factory with an o-ring made of a rubber not suitable for the high temperatures this engine regularly sees. This o-ring will harden and flatten, allowing oil to seep past it and down the engine block.
This leak is often misdiagnosed as a leak rear-main seal, as the oil accumulates at the bottom of the engine at the meeting point of the engine and transmission. Fortunately this is an easy fix.
We offer a replacement o-ring made of Viton fluoroelastomer with a temperature range exceeding 400F.
Simply remove your CPV (located on the right side of the engine, at the back of the block, near the transmission), carefully cut the original o-ring off, and replace with this o-ring, with a small amount of oil added to lubricate it for install.
The original o-ring will likely be very brittle and simply crack off using a pick or razor blade.
The CPV can be removed using a large flat head screwdriver and an adjustable wrench for leverage or preferably a flat bit or drag link socket. It can be replaced with everything still installed on the car, though it is nestled behind the rear header.
Vehicle Fitment:
All E46 M3, Z3M, and Z4M.
