I was checking the Pennzoil website and looking at different spec sheets. I noticed that the 5w oils had a lower pour point than the 0w oils. This confuses me.
It illustrates that pour point is really not indicative of anything that pertains to ICE operation. It definitely does not correlate to the cold-cranking and pumpability specification. That's why the "W" specification exists.
when they started classifying oils, the Pour Point was considered representative of engine operation.
W ratings were once based on pour point (and viscosity in Cp), then evolved to "borderline pumping"...these were found to be again, as per kschachn's post not to be representative of how oils behaved in engines.
So relatively recently, MRV (Mini Rotating Viscometer) replaced these measures, as basically how easily the oil "falls" into the oil pump pick-up tube (Dynamic viscosity maximum, and absence of yield stress)...pour point is viscosity independent, it can still be pouring, but not able to be sucked up (think straw and thickshake).
Here are some specs from Pennzoil. Which is really the best in cold weather?
PYB 5-20....CCS 5200/MRV 18000
PP 5-20.... 4000/9000
PP 0-20.... 5650/14100
PP 10-30.... 4150/8500
PPHM 5-20..... 4000/8100
PPHM 0-20..... 5380/17900
From the above list? the PPHM has the lowest numbers, so it is the best.
Keep in mind, the tests are performed at different temperatures with the 0w-xx designation occurring at -35C for CCS and -40C for MRV. You can take the 0w-xx results and roughly halve them to get the 5w-xx numbers. You can halve them again to get 10w-xx.