When looking at the viscositys, what does the various parts mean? Is the 10 in 10w30 the weight of the oil after it heats up or cools down? What about the 30 and the "w"? Also, why doesn't SAE 30 or SAE40 have the second number? Does that mean they don't change viscosity when they heat up? I was just thinking (EVERYONE watch out!) about it and I realized I had no clue. The seach function also was a tad unhelpful.