You’re explaining basic multigrade oil concepts as if anyone here was confused about them. Nobody was. I understand perfectly well what the W rating means and how viscosity behaves at operating temperature. That wasn’t the point of the discussion.
The point was that people constantly claim engines require 0W-20 because of “tight tolerances,” which simply doesn’t hold up when you actually look at the service specs. Engines that recommend everything from 0W-20 to 20W-50 often have nearly identical bearing clearances. I already pointed out several examples of this, and none of that was addressed in your reply.
Instead you pivoted to explaining that 0W-20 and 5W-20 behave similarly at operating temperature. Ironically, that actually reinforces my point. If the viscosity difference is small enough that it “doesn’t amount to a hill of beans,” then it certainly isn’t something that would suddenly make an engine fail if someone used a slightly thicker oil.
You also repeated the “tight tolerances need thinner oil at startup” line, which again doesn’t really make sense when you look at the actual physics. Even very thin oils become extremely thick when cold. A cold start on 0W-20 is still far thicker than that same oil at operating temperature, and often thicker than heavier oils at warmer ambient temps. Engines are designed to tolerate that entire viscosity swing every single time they start. That’s why the “tight tolerances” argument falls apart — the engine already experiences a huge viscosity range regardless of what oil you choose.
And the comment about wear mostly happening at operating temperature isn’t really accurate either. Most engine wear occurs during startup and warm-up, before the oil film is fully established. Once the engine is warm and operating in hydrodynamic lubrication, wear rates drop dramatically.
But more importantly, none of this addresses the original point I made about regional viscosity recommendations. The same exact engines are sold around the world with different oil charts, sometimes allowing everything from 0W-20 to 10W-30 or even 15W-40, and those engines are not built with different clearances depending on the country. The hardware is the same. The difference is regulatory environment and fuel economy targets.
So explaining what the numbers on the bottle mean doesn’t really move the conversation forward. The real question is why identical engines are approved for such a wide range of viscosities depending on market, and that’s something your reply didn’t touch at all.
If someone wants to run the manual’s recommended oil, that’s perfectly fine. But pretending the recommendation is purely the result of mechanical necessity rather than emissions and efficiency targets just ignores how modern regulations actually influence these decisions.
Also, no, a 5W-20 and 5W-30 will not be the same thickness when cold. Look at the centistoke ratings - the 5W-30 will almost always, if not always, be thicker.
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