Originally Posted By: d00df00d
I just read the thread that the first quote in the OP came from:
http://forums.audiworld.com/rs4b7/msgs/107764.phtml
Here's my take on the topic, based on nothing but an outsider's view of the debate and my own faculties of reason, such as they are:
- The carbon buildup on the valves themselves could be due to poor quality fuel and inappropriate usage (too many short trips etc.), or it could be due to the obvious oil vapor in the intake tract.
- The aforementioned oil vapor could be caused by a malfunctioning PCV system, volatization of the oil, or some combination thereof.
- Therefore, oil formulation is only one of a few possible causes of the problem.
- HOWEVER, switching oils is the easiest thing for the user to do and, if it works, addresses almost all the possible causes directly or indirectly.
Thoughts?
RI_RS4, if you're still here, does that sound about right to you?
For the Audi and VW FSI engines, you need to remember that fuel never flows over the back side of the valves
normally. It is injected directly into the cylinder. These engines all have cyclonic oil/fuel separators in the PCV system, to allow the volatile fuel components in the oil to flow through the intake, and allow the oil to condense back into the sump.
Since it is volatile fuel components that vaporize out of the oil, the "nasty" components of our poor fuel are left behind in the oil. The volatile fuel components generally burn cleanly, and would not cause significant deposits on the back of the valve. However, the volatized oil that is not condensed back into the engine, can deposit on the valve backs. This has been confirmed by removal of RS4 intake manifolds and of VW and Audi 2.0L TFSI engine heads.