Nerdy Fun: Viscosity calc tool @ startup temp.

[zaibatsu]

There seems to be a lot of interest in 0wXX oils on BITOG, but I've been aware for a while (and hopefully many of you are too) that a 0w30 and 0w40 oil can have a vastly different cold viscosities. In fact, 5w30 oils will commonly have a lower startup viscosity (at most people's ambient temps) than 0w40 oils. In this sense, SAE viscosity numbers can be misleading if you don't read further into the data.

This little calculator allows you to plug in the kinematic viscosity values (cSt@40, cSt@100) that most mfgs provide, and use them to calculate the KV at a temperature of your choice - perhaps ambient temperatures during winter and summer where you live. Very useful to compare startup performance of different oils you may be considering.

www.jiskoot.com/samplertool/viscositycalc.php

I think it is mostly useful to calculate how well an oil will flow at cold-start temperatures. For performance/economy comparisons at operating temperature, HTHS is much more relevant than KV.

 

[Quattro Pete]

Also:
http://www.widman.biz/English/Calculators/Graph.html

http://www.widman.biz/English/Calculators/Operational.html



Just have to keep in mind, since viscosity is not linear and there are other factors to deal with (such as pour point depressants), these calculations are just high level approximations, especially as you venture far below the 40C temp.

 

[ARCOgraphite]

Thanks for the calc, though I share Pete's reservation on the cals extrapolation capabilities vs actuall lab data (which seem nonexistent public-facing).
There is such a general misunderstanding of multivis Winter #'s API and SAE have to come out with an improved grading and labeling system - SOON!

 

[jstutz]

You can also play with this as well. It is just a one sheet calculator i put together years back.

https://docs.google.com/file/d/0B6pXF6fW...dit?usp=sharing

Its probably easiest to just download the excel doc and open it instead of using the google viewer.

 

[CATERHAM]

Basically kinematic viscosity calculators are plotting out the effect of the VIs of various oils, but they aren't good at determining when oils will go parabolic at temp's well below 0C.

The other thing to remember is that kinematic viscosity correlates only approximately with actual operational viscosity in an engine. It's HTHSV that correlates well with operational viscosity and does factor in the net effect of various oil's chemistry. If two oils have the same HTHSV and the same VIs they will virtually the same operational viscosities at all temp's down at least to 0C if not lower regardless of what their KV spec's are. If one oil has a higher VI it will be progressively lighter at lower temp's.
If one oil has a higher HTHSV but the same VI it will be heavier at all temperatures.

So use the plotted out KV graphs as a guide but remember HTHSV trumps the KV100 spec' in predicting actual operational viscosity.

 

[weasley]

Let's also not forget that it is CCS and pumpability viscosities that are used at low temperatures to determine the "W" number; these have a shear effect (like HTHS does) and provide a realistic resistance-to-cranking/pumping measure.

Kinematic viscosity is of low significance and extrapolation so far away from the measured values is, as CATERHAM pointed out, folly. For example, the tool calculated a viscosity for me at 750°F (when the oil will actually be smoke and coke) and at -300°F (when it will be wax).