joelukex4 wrote:
The graded WEIGHT of the oil that the number represents, is either a normal-operating-temperature weight, OR it is a WINTER weight measured when the oil is below freezing of 32 degrees Fahrenheit or 0 degrees Celsius. An operating engine will switch the oil's grade as it warms up.
Above freezing - If the oil is weighed as a 40 weight, then it is a 40 weight. Not true for multi grade oils.
Above freezing, an oil that is rated 0W-40 should pour and flow exactly the same as an oil that is rated 15W-40 because they are ABOVE FREEZING. Differences in quality from manufacturer to manufacturer are a separate conversation. If they are rated 40, then they are equivalent when above freezing, no matter what the xW rating is.
This is not exactly correct as the graded weight (40) is based on the viscosity in cSt at 100C (210F), not just above freezing. The 15W40 will be higher in viscosity until it warms up to 210F. 5W40 & 0W40 will have a closer viscosity profile.
If you want to talk about the reasons for using a 0W weight versus a 5W for BELOW FREEZING operations, then yes, there are differences and reasons to choose one or the other.
Agreed because the differences between a 0W & 5W are not important until we reach -20F.
I also use Rotella T6 and Truck Turbo Diesel.
Agreed, I don't believe its like an on-off switch where the oil siddenly changes viscosity at 32F. In fact, I believe a 5W, 10W, and 15W-40 may have slightly different viscosities even at operating temperatures due to differences in the makeup of the oil to allow them to be thicker or thinner at low temp. They all still fall into the specification for a 40 weight oil but are not exactly the same at operating temp.
FYI, Mobil 1 0W-20 and 0W-30 oils are actually higher viscosity than their 5W counterparts at temperatures above -20F(or something extremely cold like that). They advertise that its better for gas mileage but if you looks at the specs you will see it's thicker at most normal air temperatures.