I won’t go over every little thing in the video. One thing that should be said though. The manufacturers “get it wrong” NOT due to their ignorance, but their chasing of CAFE standards and credits. Fuel economy above longevity.
Don’t lose me here…
Oil viscosity
should be spec’d for the surface finishes inside the engine, in addition to the expected parameters on the Stribeck Curve. You need a film thickness (based on speed, load and viscosity) that is thicker than the difference between the peaks and valleys on the surface. This will prevent metal to metal contact (and AW additives form a backstop in conditions where this isn’t possible). That’s the “perfect world” view and one that just about every engineer would share.
Unfortunately, in the real world…oil accounts for a lot of drag and wasted energy in an engine, particularly in the bore surrounding the piston rings. The viscosity of the oil there (most closest represented in the HTHS of the oil) can be reduced to lower this drag and improve efficiency. Only slightly, and often not at all in the real world. But when you’re chasing tenths of percents for EPA fuel economy testing, it all adds up.
Reducing viscosity also increases wear, especially in a performance application. I have tracked this well in my own truck. Using a lower viscosity oil (samples 2 & 3, Pennzoil 0w40) lead to a spike in iron (bore wear). Chart is standardized for mileage.
View attachment 128780
It’s a balancing act. The OEMs need protection to be adequate enough to kick it across the warranty finish line while also chasing impossible government mandates.
Same for extending oil change intervals. They are balancing the “conservation of resources”, customer satisfaction (not being inconvenienced by frequent oil changes), and of course how the oil protects and keeps clean.
If viscosity spec and oil change intervals were based solely on what’s best for the engine, things would look an awful lot different.
We’ll leave the differences between marketing synthetics and actual synthetics for another day, although I’ve hammered that subject for a long time now anyway.
