SR5,
looking back at the (now very flawed) J300 tables, oils were graded on how much time they took to get through a standard viscometer...20 seconds give or take was a 20, 30 seconds a 30, 40 seconds etc.
Later, when they were trying to work out why some were hopeless at cold temps, they decided to pick the best of the best of the mineral grades at cold temps, and call them "winter".
Allowing a "multigrade".
Later, they tried to standardise that performance, and VII/PPD helped push them around, so they set up a variety of performance parameters that defined cranking performance and the ability to keep supplying cold oil to the oil pump pickup.
Meant that the "multigrade" concept didn't define (as university 101 alludes to) an oil that behaves like two oils, but an oil that is the final grade (30, 40), and has cold wether performance of 0W, 5W, 10W, etc.).
The craziest one that you will find on the shelf, and it's not an engine oil, but I hope helps the understanding, is a dino 85W140 gear oil.
A dino 85W140 gear oil sounds like a massively impressive quantity, compared to a synthetic 75W140, but the dino 85W140 usually has a viscosity index of 100 (or less)...it's a monograde.
looking back at the (now very flawed) J300 tables, oils were graded on how much time they took to get through a standard viscometer...20 seconds give or take was a 20, 30 seconds a 30, 40 seconds etc.
Later, when they were trying to work out why some were hopeless at cold temps, they decided to pick the best of the best of the mineral grades at cold temps, and call them "winter".
Allowing a "multigrade".
Later, they tried to standardise that performance, and VII/PPD helped push them around, so they set up a variety of performance parameters that defined cranking performance and the ability to keep supplying cold oil to the oil pump pickup.
Meant that the "multigrade" concept didn't define (as university 101 alludes to) an oil that behaves like two oils, but an oil that is the final grade (30, 40), and has cold wether performance of 0W, 5W, 10W, etc.).
The craziest one that you will find on the shelf, and it's not an engine oil, but I hope helps the understanding, is a dino 85W140 gear oil.
A dino 85W140 gear oil sounds like a massively impressive quantity, compared to a synthetic 75W140, but the dino 85W140 usually has a viscosity index of 100 (or less)...it's a monograde.
