I'm all for higher viscosity after reading and sharing an article from Industrial Lubrication magazine in which the author spelled out that the switch to the thinner motor oils:.
1. Had nothing to do with engine protection but was driven by the pursuit of gaining hundredths or tenths of a mile per gallon in laboratory engine testing. a. Car makers must specify the weight of motor oil used in an engine during EPA fuel mileage testing for the vehicles sold to the public.
b. Car makers decided to use thinner motor oils combined with low drag piston rings and low drag valve stem seals as well as other strategies to reduce internal engine friction to gain a sliver of increased fuel economy in their testing. This led to:. 1. Cylinder deactivation systems with their increased oil consumption(Honda V-6 and GM V-8's) 2. Increased intake valve carbon issues because the "LOW TENSION" valve stem seals let the thinner oil leak passed the LOOSER valve stem seals to carbonize in the heat(unless it is like a Toyota or Ford and has port injection as well as direct injection).
It is total bologna that "modern engines are built to tighter tolerances and specs and REQUIRE a thinner oil to get into those tighter spaces".
The 0W-s and the 5w-20's were not recommended and specified for reduced friction or engine durability. I am putting my money where my mouth is by running 15 w 40 in nearly everything I own. Every one of my cars has variable valve timing systems and the 15w40s have caused no issues.
Observation #1: every one of my cars consumes twice as much thinner motor oil (0W-20, 5W-20) than when I run 15W-40.
Observation # 2: the recommended oil viscosities in other parts of the world for my daughter's 2005 Honda CRV and my 2010 Scion XD are much more varied and include much thicker oils like 10W-30, 10W-40, 15W-40 and 20W-50. But in America Honda recommends 5W-20 ONLY and Toyota recommends 0W-20 ONLY for those engines!
WHY???????????