batman wrote on 06/13/19 at 07:48:27: when you see the label on oil it is very misleading , 10w40 does not mean the oil has a viscosity of 40 at operating temperature , 40 is the grade weight of oil that the oil is based on.
All oil is thick when it is cold....and thins when it gets warm....and thinner when it is hot.
The viscosity ratings of oil are tested 100 degrees centigrade for the upper rating. The oils are heated and then allowed to flow through an orifice....the rate for flow is established using straight grade oils (SAE 20, 30, 40, 50, etc). A multi viscosity oil that is rated at 40 flows through the orifice at the same rate the straight weight oil does at that temperature. This means that at 100 degrees temperature....an SAE 40 oil and a 15W-40 flow at the same rate.
The cold weather rating at 0 degrees Centigrade is not so easily defined, as it is a combination of tests. Not only do they test the flow rate of the multi grade oil and compare it to the flow rate of the straight weight oil - but they also compare the oil resistance to shear.
https://wiki.anton-paar.com/en/sae-viscosity-grades/https://wiki.anton-paar.com/en/viscosity-index/batman wrote on 06/13/19 at 07:48:27:10w40 does not mean the oil has a viscosity of 40 at operating temperature , 40 is the grade weight of oil that the oil is based on. Oil does get thicker as it cools and that IS the problem. the actual viscosity of your oil at running temp is about 10 to 14 . the viscosity of the oil at 75 degrees can be about 250+ for a straight 40 wt.,100 for 10w40
The viscosity of an oil at operating temperature is approximated by the upper number of the multi viscosity rating at 100 degrees centigrade - which is 212 degrees......what they consider as an operating temperature for water cooled engines. To say that a 40 weight oil at 100 degrees has a viscosity of 10-14 at this temperature is misleading - as you have not stated what temperature the 10-14 weight oil is at (I understand you are implying the 40 weight oil is thin when hot....I get that). However the engines are designed to run with the engine oil being thin when hot.
I also understand that oil is thick when cold, and it does not flow was well when cold. However the difference in thickness between a 5W, 10W, 15W and 20W oil is not significant at summer temperatures, and really isn't a contributing factor in which motor oil to buy for summer use......however some folks argue that more additives are used to lower the winter use rating, and those additives take up space that would normally be occupied by oil molecules - thereby reducing the lubricating value of the oil (Theory is a 15W-40 oil will have more oil and less additive than a 5W oil and provide better lubrication).
So that is how I feel and what my beliefs are based on - I am using Rotella a T4 15W-40 in my tractor, and T6 5W-40 in my cars and motorcycles. If somebody wants to use a 20W-50 in the Savage in the summer...I am OK with that as the factory says it is OK in the owners manual - they may want to consider a thinner oil if they ride in cool temperatures.
Here is a video to satisfy your interest in what motor oil looks like at -30 degrees.......not a good day for riding your motorcycle, and definitely the kind of weather that requires a block heater or warm garage.
https://www.youtube.com/watch?v=MVn5OzuHtjg