sedanman said:
My info comes from a retired lube engineer from Texaco Research Center, your opinion is based on what exactly?
Well for starts, I just grabbed this from the post above yours.
"But petroleum based motor oils usually have Viscosity Indexes of less than 100 because they tend to thicken more at the colder temperature due to the paraffin despite the addition of Viscosity Improving additives."
Another regarding synthetics.
"Synthetic oil has good mechanical properties at extremes of high and low temperatures. The molecules could be made large enough and "softer" to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allows flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a much improved viscosity index over the traditional petroleum base."
"Multi viscosity oils work like this: Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot."
There's a small sampling of what my "opinion" is based on. Now it's your turn