Posting my latest UOA of Pennzoil Platinum 5w-30 per the request of a fellow Subaru owner who regularly posts over on the Bob is the Oil Guy (BITOG) forums, and asked me to post a copy over here on NASIOC as well.
2005 Subaru Impreza WRX STi
COBB Stage 1 (ECU reflash providing an additional 25 HP)
Gasoline (Unleaded); 92 Octane
OEM (Part #15208AA080)
Make-Up Oil Used:
One treatment of Techron fuel system cleaner approx. 200 miles prior to oil change.
Oil in Use:
08/03/07 - 02/24/08 (206 Days)
I would consider myself a semi-aggressive driver in general. Vehicle is used for commuting 17 miles to/from work, 90% highway driving at speeds between 60 and 80 MPH. Also driven on weekends around town. No racing or other track driving.
Wear continued to increase in the latest sample from your STI, though nothing is high enough to point to an obvious mechanical problem developing. If you did any hard driving or racing on this fill that could explain the increase. A trace of fuel was found but this level isn't a problem. The viscosity of the oil remained normal, despite the fuel dilution, and no other harmful contaminants were found. The TBN read 2.8 so you had some active additive remaining. At 33,232 miles we have no new problems to report.
My potassium level continues to drop, so I feel pretty sure that I don't have any major coolant leaks in the engine. I will continue to monitor it and hope that it stays the same or drops off further toward zero.
The air filter was replaced as part of the 30,000 mile service ... no change in silicon level. At least it stays pretty consistent from UOA to UOA.
I have to admit that I'm slightly underwhelmed at the results of this UOA. Slightly worse iron and copper levels, slightly better lead level. The low flashpoint is disappointing...perhaps I do have some fuel dilution issues.
BTW, the oil was replaced with more Pennzoil Platinum 5w-30 and an OEM oil filter. I'll plan to run it around 5,000 miles and then I think I'm going to switch back to German Castrol as I have a decent size stash to use up.
I don't post much these days on NASIOC, so I may not respond to any questions posted here for quite some time. Feel free to comment in my thread over on BITOG if you'd like.