Originally Posted By: TTK
Never the less, is BITOG the only source of this claim?
No. This document covers the entire topic in great detail:
Link to Google Book
From page 9:
Quote:
The actual viscosity characteristics of motor oils at low temperatures are a matter of considerable technical interest, but unfortunately precise determination of low temperature viscosities is far from simple. Low temperature viscosity measurements on motor oils in conventional Saybolt or Kinematic viscosimeters produce fictitiously high results, and often indicate complete solidification, since gravity is the only force to produce oil flow. A variety of mechanically drive and pressure viscosimeters have accordingly been used to determine low temperature viscosities under the greater forces (shear stress) and higher flow rates (shear rate) which are more nearly comparable to the conditions set up in engines at the time of cold starting.
*snip*
Quote:
Fig. 4 shows similar viscosity data on a typical commercial SAE 5w-20 motor oil of 145 Viscosity Index and -40F pour point. At temperatures of 0F and lower, there is a marked deviation between measured and extrapolated viscosities at all rates of shear.
If you look at the picture you can see it start to bugger off at around 10F. (-12C) That's for this particular lubricant. For this same reason I won't extrapolate CCS/MRV up past -15C, as they are cold temp performance tests (you can halve CCS/MRV to approximate its viscosity in 5 degree increments). I believe it was Tom NJ (don't quote me) who said that for most oils you can use the calc down to -10C, some to -15C. I error on the side of caution and don't trust them below 0C as there is that variability there. However Tom's (IIRC) statement appears to be supported by this paper so it may be safe to say you can't trust the calc below -10C
This source is:
The Role of Engine Oil Viscosity in Low Temperature Cranking and Starting: Prepared Under the Auspices of the SAE Fuels and Lubricants Activity
By Yong Zhou
Quote:
Professor Yong Zhou is a recognized expert in the field of non-linear difference equations and their applications in China. He was Editor-in-Chief of Journal of Dynamical Systems and Differential Equations over 2007-2011, and is present Guest Editor at Optimization (T&F), Nonlinear Dynamics and Journal of Vibration and Control (Sage), and at Elsevier former Guest Editor of Computers & Mathematics with Applications over 2010-2012 and Applied Mathematics and Computation over 2014-2015.
