This is such bullsh!t... stop it. Do you even know what "tight tolerances" they mean... no you don't... It's not that the rod bearings, mains and piston to wall are that much tighter. ... they aren't. What it means is manufacturing wise they are supposed to be more uniformly built from better equipment with more repeatability. Because of those supposed requirements you can run water consistency oil and still be blessed to build oil pressure. They tightened up their tolerance to error... You need clearance regardless to deal with with thermal expansion... that hasn't made engines suddenly need zero clearance between a bearing and a journal. Engines built 35 years ago can easily be machined with the same physical tolerances but magically they are okay to run with higher viscosity oils.... nope! The only argument I have ever seen that may present some validity is the cam phasers because depending on design oil pressure advances and retards the cam or cams. If it changes ant amount it throws the process out..... but that's it. Enough with this tight tolerance rubbish already!