Yes, I agree 100% that 100 F isn't a "fall off the cliff" number. That
wasn't my point. The point is that the 10W30 shows a higher temperature
suitability than does 5W30 even though the "hot" viscosity number is the
same for both oils.
I was getting my BMW motorcycle reading for riding and decided to check
the owner's manual for it and found the exact same thing. It shows two
multigrade oils with the same upper end viscosity number, but different
"winter" numbers and the oil with the lower "winter" number is also
limited on the high temperature end whereas the other oil isn't. I
think these were heavier grades with a 40 or 50 weight upper end, but
the chart was exactly analogous to the Chrysler chart. So, I personally
do not think one can say that just because the upper viscosity numbers
for two different range multigrade oils are the same, that they have the
same performance in hot conditions.
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