On oil table's such as the one below, why does a 20/50 have a higher temp rateing than a 10/50? The two higher number's (50) are the same. The lower number's seem to follow form, but the higher number's that are the same, seem all at sea
Perhaps they are concerned with the lower end of the temperature spectrum. The polymers which make the oil thicker at higher temperatures will shear apart with use. A higher viscosity base oil will not lose viscosity at high temperature to the same degree as the thinner oil. Do you need to worry about it? Probably not.
I don't ever recall an oil container labeled 10w50 on a shelf in the 35 odd years I have been buying oil..... Mike
<Oil Nerd Hat On> Multi-weight oils start at the lower number. Additives are added to make the oil have properties of a thicker oil at higher temperatures. A 10W50 weight oil is 10 weight oil with a bunch of additives added to make it behave like a 50 weight oil when hot. Since 20W50 starts life as a 20 weight oil, less additives are needed to make it behave like a 50 weight oil when hot. This means that 10W50 weight oil would break down and fall out of a 50 weight range quicker than 20W50 oil. In addition, there are acceptable ranges of given weights of oil. A 10W50 oil would be on the low side of a 50 weight classification when hot. A 20W50 oil would probably be in the midpoint of a 50 weight classification when hot. Example to help illustrate what I mean: Mobil 1 0W40: Viscosity at 100 degrees C is 13.5 Mobil 1 5W40 Diesel: Viscosity at 100 degrees C is 14.5 Mobil 1 10W40: Viscosity at 100 degrees C is 14.7 Mobil Delvac 15W40: Viscosity at 100 degrees C is 15.0 SAE range for 40 weight oil at 100 degrees C: 12.5 to 16.29 As you can see, all of Mobil's 40 multi-weight oils meet the SAE range for 40 weight oil, but they fall in different places within that range. The SAE viscosity range for 50 weight oil at 100 degrees C is 16.3 to 21.89, which is very wide considering that 30 weight oil is only 9.3 to 12.49. Your bike's manufacturer probably knew this when they wanted the bike to have thick oil which is why they didn't recommend an oil on the low side of the SAE 50 weight range at high temperatures. At the end of the day, its your bike and you can use whatever you want as oil. Just don't expect warranty coverage if you go outside of the manufacturer's oil specs. <Oil Nerd Hat Off>
i learned back in those early VW days that running 20w-50 in the winter means i had to push-start the car.
I just get mine at the local, small town, H-D shop. The shop does sponsor a few racing teams, so that my be why they carry the Motul.
What is that oil chart for ? Where 10w-40 only goes to 42 degrees F............HD or other hot running air cooled engine ?????
It's for oil, and it's somewhat out of date. Dosen't matter what vehicle you run the oil in; all that matters is that you chose the right oil for the service conditions.