Viscosity vs Temperature Formulas.

[Al]

Just messing around the other day and I came up with this:

Here are the calculations I made the formulas from here:
Function Equation Finder from Points Table - Online Calculator (dcode.fr) Select "Parabola"
T is horizontal line. V (viscosity- cSts) vertical line

Mobil 1 0W-20 ESP
V=8.5 at 100C
V=45.7 at 40C
V= .00867T^2 - 1.833T +105

Mobil 1 5W-30 ESP
V=10 at 100C
V= 59.7 at 40C
V= .01205T^2 - 2.516T+141

Mobil 1 FS 5W-40
V=13.2 at 100C
V=81 at 40C
V= .01655T^2 - 3.4477+ 192

Full synthetic motor oil | Mobil™

 

[twX]

Those formulas will only work at temperatures between 40C and 100C, and they'll have some error.

Here's a tool from Widman that allows you to graph an oil's viscosity at any temperature based on KV40 and KV100. If you were to use the equation finder with more data points taken from the Widman calculator, you could probably derive a more accurate formula that works over a wider temperature range.

 

[OVERKILL]

Those formulas will only work at temperatures between 40C and 100C, and they'll have some error.

Here's a tool from Widman that allows you to graph an oil's viscosity at any temperature based on KV40 and KV100. If you were to use the equation finder with more data points taken from the Widman calculator, you could probably derive a more accurate formula that works over a wider temperature range.

Yup, though "any temperature" isn't accurate, visc calcs become inaccurate below 0C and progressively moreso the further you go from it.

 

[Brian123]

Those formulas will only work at temperatures between 40C and 100C, and they'll have some error.

Here's a tool from Widman that allows you to graph an oil's viscosity at any temperature based on KV40 and KV100. If you were to use the equation finder with more data points taken from the Widman calculator, you could probably derive a more accurate formula that works over a wider temperature range.

I have been using that tool from Widman to look at what the Viscosity would be at 122C since this is the highest Oil Temperature I have seen on my Kohler 7000 Series Engine. I am putting in many different oils and I will probably pick either a 5W-40 or 10W-40 oil.

10W-30 is just not going to cut it.

 

[ka9mnx]

I have found 10w-40 is best for all my OPE.

 

[ZeeOSix]

Some in depth info.

https://www.stle.org/files/TLTArchives/2021/03_March/Lubrication_Fundamentals.aspx

 

[ZeeOSix]

Here's another calculator. Probably using the same equations as the Widman calculator. User the "Custom" pull down option for other oils.

https://fluidpower.pro/temperature-viscosity-chart/

 

[weasley]

Just messing around the other day and I came up with this:

Here are the calculations I made the formulas from here:
Function Equation Finder from Points Table - Online Calculator (dcode.fr) Select "Parabola"

You are forcing it to be a parabola, when it isn't.
https://en.wikipedia.org/wiki/Temperature_dependence_of_viscosity#Models_for_kinematic_viscosity

 

[Al]

You are forcing it to be a parabola, when it isn't.
https://en.wikipedia.org/wiki/Temperature_dependence_of_viscosity#Models_for_kinematic_viscosity

A parabola is nothing more than a 2nd order equation in the range you want to use it for
But the easiest is to just go to say Mobil 1 and look up the viscosities at 40C and 100C You then merely draw a straight line with Temp on the x axis and viscosity on the y azxis (log) using semi-log paper. You are good to go from 150C to 0C. And the equation here is spot on.