Duke48

Hello,

I would like to know if steel cylinder inserts require higher viscosity (to form a thicker oil film) at 100C?

Let's say that for the given engine with Alusil coating 18.5cSt is an optimal value, will the same engine require for instance 21 cSt when switching to steel cylinder bores? I'm aware when switching to steel the engine is more loosely fitted when cold, I don't know how this translates to warmed-up temps.

V2Rocket

While there is likely some effect of oil weight, in reality this is why steel bores have larger piston-wall tolerance than alusil.

Published oil Cst is averaged over a batch but the bottle of oil you put into the engine may or may not match the spec exactly.. so hard to be too worried about it