Did you see this part in that link?:
"The behavior of the most fluid oil (0W5) is quite different. At relatively great clearances its viscosity is too low to create hydrodynamic force sufficient for maintaining the required level of min. oil film thickness. This effect is the most prominent at low rotation speed 2000 RPM. The greatest value of oil film thickness is achieved at the lowest clearance of 0.0004” (1/5000 of the bearing diameter)."
Show me one passenger car on the road that has journal bearing clearances of 0.0004".
What this says, and what the corresponding graphs show, is that running a very thin oil in anything but a super tight bearing is going to not provide adequate MOFT to protect the bearing from wear. The graph also shows that all thicker oils above 0W-5 gives more MOFT, regardless of the bearing clearance.
And note (as I mentioned before) that low RPM makes MOFT even less
. So even just "cruising around" at low RPM with very low viscosity is giving the smallest MOFT, especially in bearings that are not super tight - again, it's worse to run thin oil in large clearances than it is to run thick oil in tight clearances.
Most passenger car journal bearings are in the 0.0015-0.0020" range - about where the peaks of MOFT are shown for the two thicker oils in the graph.
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