Hi Subsearobot (and everyone else who's interested)
I thought you might find some use for the attached calculator. It's a tiny little spreadsheet with a huge calculation in one of the cells which allows you to estimate (to within ±10%) the viscosity of an oil at any temperature. Simply put in the viscosity at 40°C and the viscosity at 100°C (to enable the spreadsheet to calculate the characteristics of the oil) and then put in the temperature at which you want to know the viscosity.
Most fluid datasheets will give you the viscosities at these two temperatures, but if you haven't got the 100°C viscosity then the 'work around' goes like this:
Let's imagine you have the viscosity values at 40°C and 0°C.
1) Put the 40°C viscosity value in the spreadsheet.
2) Guess a typical number for the viscosity at 100°C and put that into the spreadsheet.
3) Ask the spreadsheet to calculate the viscosity at 0°C - the number it gives you will be wrong because one of your viscosity values was a guess.
4) Then use the "goal seek" function to make the newly calculated viscosity at 0°C equal the datasheet value by changing the cell that contains the 100°C guess.
5) You will then have a value for the 100°C viscosity that enables the spreadsheet to work properly.
The values of pour point temperature and flash point temperature are only used to stop the calculation from giving silly answers for viscosity at extremes of temperature - try it and see. If you don't have these two values then just put in some dummy numbers: say -100°C for pour point and 800°C for the flash point.
I've deliberately saved the file as an old version of Excel because not everyone has the latest version available to them. I'm also sure that there will be much more sophisticated versions available on the internet somewhere but this little calculation has served me well for years and I'm happy to share it.
DOL