Need Help Calculating Cold Viscosity of Oils

[BlazerLT]

Ok, here are the two oils in question.

Mobil 1 5w50

cst @ 40c = 105
cst @ 100c = 17.3
Viscosity index = 153

Mobil 1 5w30

cst @ 40c = 64.8
cst @ 100c = 11.3
Viscosity index = 169

Does anyone know the calculation for say the viscosity at -25c?

Could someone help me out here?

 

[dakota99]

5w50 @ -25C = 6547
5w30 @ -25C = 4211

i hope that's right.

 

[Captain_Klink]

they cannot be calculated, these are measured values, and are published on the internet by the manufacturer.
http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil_1_0W-40.asp

will show that the MRV for 0w40 Mobil 1, at -40C, is 26242.
just go to the mobil site, select the oil you want, and they will list what you're looking for. the same method is used for oils made by the different companies. use google search, put in the name of the oil, and viscosity. this should usually lead you in the right direction.

 

[Geonerd]

Klink is right, there is easy way to calculate the value. Once the temperature drops to the the freezing point of any of an oil's innumerable ingredients, the oil becomes a slurry of sorts and the viscosity vs. temp curve goes bananas.

I suspect that most oils are past this 'initial freeze point' (for want of a better term) by -25C.

 

[Cup of Joe]

Why not graph them on widmans viscosity graph. You can adjust the minimum temperature to your operating enviroment in C.

http://www.widman.biz/Seleccion/Viscosidad/Conversiones/Graph/graph.html

 

[Geonerd]

Oops!

I meant to say "there is NO easy way to calculate the value."

 

[Audi Junkie]

The visc calc, while not "accurate" will clearly tell you which oil is thicker or thinner. Down to -25f, you are better off just referring to the CCS sheets, where a 5w30 is thinner by definition. Closer to 0f, the visc calc is more helpfull.