- Aug 6, 2021
They say that a 0W20/0w30/0W40 have the same cold viscosity. Unfortunately, this is wrong. A 0W40 is about three times as thick as a 0W20 at -5/0/5/10C. If I start an engine at 10C with a 0W40 then it is about as if I start the car with a 0W20 at -10C. There are already considerable differences.Please, let's have an academic and respectful discussion here.
The one single compelling colossal metric that convinced me to be in the "thick crowd" is the HTHS wear graph which shows running any oil lower than HTHS 2.6 (0W-20) results in exponentially higher engine wear.
Please let us know why the ultra thin crowd ignores this metric and why you feel this metric is not important.
If you are concerned about engine wear at engine startup, 0W-8, 0W-16, 0W-20, 0W-30, and 0W-40 all have the same thin viscosity at engine startup. So the focus of this discussion should be engine wear at temperatures higher than 100C (212F) and why a thin oil is beneficial during high temperature, high RPM, high sheer, heavy load conditions. Typically the coolant temperature is around 100C in most cars during normal operation, but the bearing temperatures can go much higher (as high as 150C). In this scenario, all oil becomes thinner due to the heat, and there is a danger of metal on metal contact when the film thickness gets too thin. So that is why using a HTHS oil >= 3.2 is beneficial, and 3.5 being optimal. This gives a cushion of protection when the oil sheers to the next lowest grade as the oil ages during an oil change interval.