Originally Posted By: gfh77665
The "w" stands for winter, and multi-visc oils try to stay THIN as the temps drop. Where (what temp) is that point where that effect happens? That is what am referring to.
No.
While the "W" designation does denote Winter, it doesn't mean the oil "gets thin".
What it means is simply that the oil RESISTS thickening more than a straight-weight oil like SAE 30 for example.
The CCS and MRV values were posted earlier, and they are what define the "W" rating. The lower the MRV and CCS numbers, the less steep the viscosity slope going from cold to hot; the less change there is between the (thicker) cold viscosity and the oil's hot viscosity.
On top of that, there is VI, which is the viscosity index, which gives you the curve/slope for the oil's viscosity between 40C and 100C. This can be extrapolated in either direction, however it doesn't give you accurate information below 0C. This is where MRV and CCS are valuable.