Oil is the lifeblood of our engines. Without it, our motors would seize, and we would have a very heavy, very expensive paperweight. Oils have changed dramatically over the last 50 years. New compounds have been derived, replacing some of the older, more recognizable, designations. One of the casualties of these changes has been the amount of zinc in the oil. Zinc is an excellent anti friction agent, but unfortunately is also a pollutant. The viscosity of each oil is measured on a few different scales. The engine oils are measured on an SAE crankcase scale. Gear oils also have a separate scale.
Multi-weight oils, like those commonly seen today, are labeled “10W-30” and similarly. These are made by adding various polymers to the oil, allowing it to have a different viscosity at different temperatures. A neat little trick to remember is that in the case of our “10W-30” example, it would be a “10” weight oil that will not thin out any more than a “50” weight oil would.
Some oils will have the same viscosity as others, but this does not mean you can interchange them. The different compounds added to each may have a disastrous effect on your engine. Therefore, it is always best to use the manufacturer or rebuilder recommendation for your engine. These will often include variables such as the local climate and driving style. Located at the bottom is a temperature chart you can use to find recommended oil for your climate. Many manufacturers also suggest changing the weight of your oil as spring and summer change to fall and winter, and change back as fall and winter give way to spring and summer.