[cody]

Originally Posted by cody

I read both articles at this link, but the one in the sidebar is far more insightful the other.

I just reread the article and it's wrong.

Most autocross and hillclimb cars roll to the starting line with cold oil: Not quite freezing temps, but far from the 212 degree mark. The 20W50 oil is likely to behave closer to its 50-weight rating in these conditions, so it’s doing precious little in the way of lubrication. The thick oil isn’t able to penetrate deep into the engine, and the results can include spun bearings and thrown rods.

pretty much directly contradicts

Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature. This page from the Sci.Electronics.Repair FAQ offers the following very interesting description of how the polymers work:

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.

http://auto.howstuffworks.com/fuel-e...estion1641.htm