Unlike bearing lubrication, cylinder - ring lubrication is very complicated that involves all regimes of lubrication, including boundary, mixed/elastohydrodynamic, and hydrodynamic.
While thicker oil tends to provide a thicker oil film in general, especially in the hydrodynamic region, it turns out that the oil flow by the rings is very complicated and cavitation -- a complete break in the oil film -- is always present and inevitable regardless of the viscosity and operating conditions.
It turns out that the length of the cavitation (oil-starved) region is proportional to (see the second article):
Length of the cavitation ring section ~ (RPM x viscosity)^0.3
^0.3 represents the 0.3rd power, which reduces the effect of the RPM and viscosity. For example, if you increase the viscosity by 2, cavitation length increases by 23% and not by a factor of 2.
Typical cavitation lengths (oil-film-starved sections) are around a millimeter or less.
This means you need to strike the right balance between cavitation and oil-film thickness. Going thicker won't necessarily reduce ring wear. Cold engines could be even more problematic for thicker oil.
The first link is open access:
https://www.sciencedirect.com/science/article/pii/S0301679X15001760
Not open access:
http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468067
So, it's something to think about before you go arbitrarily thick to reduce ring wear.
While thicker oil tends to provide a thicker oil film in general, especially in the hydrodynamic region, it turns out that the oil flow by the rings is very complicated and cavitation -- a complete break in the oil film -- is always present and inevitable regardless of the viscosity and operating conditions.
It turns out that the length of the cavitation (oil-starved) region is proportional to (see the second article):
Length of the cavitation ring section ~ (RPM x viscosity)^0.3
^0.3 represents the 0.3rd power, which reduces the effect of the RPM and viscosity. For example, if you increase the viscosity by 2, cavitation length increases by 23% and not by a factor of 2.
Typical cavitation lengths (oil-film-starved sections) are around a millimeter or less.
This means you need to strike the right balance between cavitation and oil-film thickness. Going thicker won't necessarily reduce ring wear. Cold engines could be even more problematic for thicker oil.
The first link is open access:
https://www.sciencedirect.com/science/article/pii/S0301679X15001760
Not open access:
http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468067
So, it's something to think about before you go arbitrarily thick to reduce ring wear.