justin_o_guy2 wrote on 11/01/19 at 07:24:42:It's been my understanding that multigrade oils flow at low temperatures easier than once they are warm.
That is not accurate.
All oils thicken when they are cold....and get thinner as they warm up. No oil thickens as it gets warm (or hot). A hot 30 oil will be thinner than a hot 40 weight oil......and a both will be thinner than a hot 50 weight oil. The 20/30/40/50 viscosity number is measured at the boiling point of water (100 degrees centigrade or 0 celsius).
The winter cold weather "W" rating of a multigrade oil is tested at 0 degrees centigrade (-17.8 degrees celsisus). An oil that has a 5W rating will flow easier cold than one that is rated 10W.....and 15W and 20W are a bit thicker yet and a bit harder to flow at cold temperatures.
The additives in a multi-grade oil can do one or both of the following:
1) For cold weather - the additives can help to prevent an oil from thickening excessively when they are cold.
2) For hot weather - the additives can help prevent the oil from thinning. (The additives do not make the oil thicker).
To make this even more confusing - the winter "W" rating is also not a pure viscosity measurement, and it also includes a test to see how much resistance the oil provides when a shaft is turned and the the force measured......some additives reduce the turning force required in cold weather. (The W rating not only has parameters for flow - but also for resistance to turning in a plain bearing).
The bottom line is that cold oil resists flow more than warm or hot oil does, and you should use an oil with a 'W" rating that is appropriate for the weather you ride in .......as well as the warm temperatures. This time of year our weather can be in the 20's in the morning when you go to work - and in the 70's when you come home.....this is the kind of environment that Multi-Grade oils were made for.
https://www.lubricants.total.com/consumers/maintenancetips/Oil-viscosity-and-...https://www.castrol.com/en_us/united-states/home/motor-oil-and-fluids/engine-...In the following link you will see that the viscosity of all the listed oils thin as they warm up.
https://wiki.anton-paar.com/us-en/engine-oil/