Buster,
The standard CCS test temps are supposed to represent a conservative low temp limit for use of a particular SAE grade. For years the German engine manufacturers have used them in precisely this manner. So you'd see them recommending -10C/-15C/-20C/-25C, etc as explicit low temp limits ....
For example, until 1999, VW/Audi/BMW/Mercedes used to recommend the 10w-40/10w-50 grades down to -20C/-4F, the SAE,15w-40/15w-50 grades down to -15C/+5F and the 20w-50 grade down to -10C/+14F. They allowed the use of 5w-50 oils for all temp ranges ....With modern fuel injection systems, engines start at lower temps and with thicker oils than every before. Most of the German auto makers now recommend low viscosity synthetics, ie 0w-30 through 5w-40 for all temps. However, some of this is so you can use the same oil year round, even if you live in Alaska, and some is based on fuel efficiency concerns.
Common sense indicates that you'd like the oil to be as thin as possible to enable easy cold temp starting and to optimize fuel efficiency during the warmup phase. However, most lube engineers will tell you that if the oil is thin enough to allow the engine to crank easily, it's safe to use under those conditions, regardless of the SAE grade.
The borderline pumping temp (BPT) is defined by the SAE at the point where the viscosity of the fluid thickens to 60,000 Centipoise - that's about ten times the CCS limit for any SAE grade. If the fluid is thicker than this you'll get cavitation and extremely high engine wear due to lack of oil flow ....
Tooslick
Dixie Synthetics
[ November 25, 2003, 07:32 AM: Message edited by: TooSlick ]