Last weeks article about the impact on lubricants of low speed pre-ignition said researchers found that higher viscosity PAO showed higher LSPI. Ken Hope of Chevron Phillips Chemical Co. pointed out that this reference is comparing 8 cSt PAO to 4 cSt PAO.
Ken Hope wrote: When I think of higher viscosity PAOs, the 40 and 100 cSt materials come to mind as well as the recent mPAO materials that Chevron Phillips Chemical and others produce. In rereading the Takeuchi paper from 2012 [I] found that the higher viscosity PAO they used was a PAO 8 cSt, which is higher than the 4 cSt oils but not considered a high viscosity PAO in the traditional sense. So this could be a point of confusion. The actual quote from the Takeuchi paper on this point was:
The effect of viscosity was determined using two viscosity grades of PAO (4cSt, 8cSt) and showed that that the higher viscosity PAO caused higher LSPI frequency than that for the lower viscosity PAO. – Takeuchi et al / SAE Int. J. Fuels Lubr. / Volume 5, Issue 3 (November 2012, page 1020)
Of course, a high viscosity PAO wouldnt likely be used in this application anyway so it may be a moot point or at least a fine point that few may notice. Nevertheless, your article caused me to take another look at the 2012 research, which I hope others will also do as people address this important issue on engine reliability.