justin_o_guy2 wrote on 11/01/19 at 18:15:50:


Jog:

That is not how the 10 viscosity is measured.....or how the 30 is measured.  No oil becomes thicker when warm - all oils become thinner as they warm up.

Look at these charts for the mulit-grade oils - it shows that all oils thin as the oil warms up.
https://wiki.anton-paar.com/us-en/engine-oil/


The "Multi-Grade" ratings come from taking measurements of the oil, and assigning numbers that correspond to the way a "straight weight"oil would behave at that temperature.  If an oil has a 5W rating, then it means that the Multi-Grade oil has the same characteristics that an SAE straight 5 weight oil would have at that same temperature (0 degrees centigrade, 32 F).  The Multi-Grade oil is then tested at 100 degrees centigrade (212 F), and the oil is assigned a value that corresponds to the characteristics of a straight weight SAE oil at that same temperature.

Mulit-Grade oils don't get thicker as they heat up - they just don't thin out as much as a straight weight oil would.  If you doubt this and need proof - think about what happens when you change oil in a cold engine vs. a hot engine.  If you take out the drain plug when the engine is cold, the draining oil comes out a bit syrupy and drops pretty much vertical into the drain pan - but if you change the oil in a hot engine the oil shoots out the drain plug and you have to catch it about a foot away from the drain hole!

https://www.youtube.com/watch?v=Hb6CX_rWoIA

And if you want to make it even more confusing......the testing done at 100C and 0C for viscosity is not even done the same.  Look at information in the table shown below.  The top table shows what the viscosity is for oils at 100C - and a 40 weight oil has a kinematic viscosity of 12.5-16 mm/sec squared - that is obtained by flowing the oil through and orifice and comparing the flow rate and matching it with the flow volume of a straight weight oil.....in this case the oil flow at the same rate as an SAE 40 weight oil would at 100C.

The cold weather characteristics of a Multi-Grade oil are obtained by using the  oil in a simulated engine (bearing and shaft), and measuring the resistance to turning the shaft - and also pumping the oil through an orifice to determine the resistance to flow at 0C.  These values are then compared to how a straight weight SAE oil behaves at 0C, and assigning a matching "W" rating to the oil. If you look at the second chart you will see both a cranking and pumping viscosity is listed.

https://wiki.anton-paar.com/us-en/sae-viscosity-grades/


It is unfortunate that so many people describe the oil as "thickening" when it warms - the truth is that all oils thin as they warm and thicken as they cool.  The Multi-Grade oils just don't thin as much as a straight weight SAE oil......and at the elevated temperatures they behave like an oil with a higher viscosity (but the oil has not become thicker).

And if you still aren't a believer - buy 2 quarts of that magical thickening oil and put one quart in the freezer and one quart in a pot of boiling water.......then remove the caps and see which one pours faster.  I will bet you a 6 pack of PBR that the hot oil pours faster than the cold oil.

 pressure X volume , Divided by temperature  is a standard thermodynamic equation . this means that if the temperature remains the same  ,and increase in pressure must show a decrease in volume(flow).    That's why 10w 40 oil is used in our bikes rather than 20w 50 and does a better job.    20w oil will be thicker on cold startup and cause more wear .   50 grade oil will have higher pressure ,but decreased flow do to the oil passages being of fixed size.  the moving parts like our flat rockers and cam lobes don't touch only because of the layer of oil that passes between them, the thicker the layer the  the better.  oil pressure if high enough ,is less important than flow  . 10 w40 will provide a thicker layer between parts and the higher flow rate will carry away more heat ,it's other job, and important in our air cooled motors .Bottom line thinking that a 20w50 oil will protect your motor better than 10w40 the factory recommend is a mistake . As Dave said Rotella T6  5w40 is one of the best oils you can use in your bike . Decreased wear at cold startup and increased protection when warm as compared to a50 weight oil which will show an increase in your oil temperature . A 5w30 oil can be used  down to -20F  but only as high as 88F .(Alaska?).

Yeah, these people will go
Oil School
on ya in a second..

Gary in NJ wrote on 11/03/19 at 04:03:46:
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LOL  Hasn't been a good'ol OIL WAR in a while.