Initial comment:
Remember that street oil has two viscosity ranges, like 5W-40. When the oil is cold, the viscosity is low and the oil is "thin". Do you really want to be driving around with an oil that thin? Unless you're making a qualifying run, you do not.
Questioning of initial comment:
Perhaps it's the way I'm reading this, but you seem to imply that 5W40 is thinner when cold than it is when hot. Hopefully that's not what you mean.
Questioning of initial comment:
Here's an admittedly unscientific experiment conducted by a father and his sons that clearly shows 5W-40 oil is significantly thicker at 0 degrees celsius than it is when it's approximately 100 degrees celsius.
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It seems the challenge side here is out to prove that oil is thinner when hot than cold. I ‘assume’ the initial comment was, made loosely, in relative terms, intended to mean the same, as follows.
That is, in general, given the two numbers in a multi-viscosity oil, when oil/temp is cold, an oil with the lower grade number would be thinner at that same lower temperature than would an oil with the higher grade number.
More specifically, I think he was referring to the 5W grade, and its properties, a ‘thinner’ starting/cold temp grade compared to other grade options on the grade scale, and so even thinner (too thin) when it heats up.
I don’t know that he spoke to the protection to the 40 grade at higher temps, rather was just making a point about the 5W cold/starting oil temp grade itself.
Maybe both sides are actually on the same page, stated in vastly different ways, on that point anyway!
Just a thought…Brent