Back when I was a kid working at my 1st job in the gas station, the 10W-30 oil was a new concept, before then it was usually straight weight oil that had to be changed every spring to the heavier weight and every fall to the lighter weight. The 10W-30 was a pretty hard sale to those that were used to the straight weight, but it finally caught on. Then they came out with the 10W-40 that was suppose to be better for the hot summer then the 10w-30 was. Then the racing oil in the 20W 50 showed up.

Back in the straight weight oil days, almost no one used straight 40 weight oil unless the motor was really wore out. The guys at the gas station were pretty surprised by how many people jumped on the 10W-40 oil after it was so hard to sell them the 10w-30.

Currently, the auto manufacturers are pushing the 5W-30 and now the 0W-20 for modern "tighter" motors. As the people adjust to those very thin modern motor oils, the thicker older oil grades are going to fall by the wayside, except for the people that have older cars. That 20W-50 is pretty much gone except for real racing motors. The 10W-40 is going to be the next causality. The 10W 30 may survive for a while longer because a lot of people have older cars, and some (like me) just can't grasp the 0W-anything oil in anything I want to drive down the road. I don't live where it is extremely cold, I don't like that really thin stuff they are passing off as oil, I don't have any motor that is that "tight".