Explain this - turbo "issues"...

steved · 07-02-2009, 01:17 PM

Alright...found this interesting to say the least...

I have been running Schaeffer's Series 9000 5w40 (a PAO oil) for the past few miles (around 30k). Ever since I put it in, the turbo has wavered (slow pulsing) at light throttle...almost like the waste gate control wasn't working properly, and was "hunting" for the right position. You couldn't feel it, may have been able to see it in boost pressures, but you could definitely hear it. The wavering has been with me for the past 30,000 miles...not something that changed after a while, it started with the oil change (at that point I assumed it was coincidence).

Fast forward to Monday, and I decided to change back to conventional Rotella 15w40 since I was seeing no real benefit from running Schaeffer's. Turbo immediately quit wavering. I have driven it 300 miles since putting Rotella back in...not a hint of wavering. I could make it waver on command prior to this.

The viscosity of the Schaeffers is quite a bit higher than Rotella, as reported on my UOAs. Both oils tended to show similar characteristics (wear metals, etc.). The only outlier was an slight increase in lead running Schaeffers.

Why would simply changing oil (nothing else was touched) cause a change in turbo operation?