Oil weights: what are they and are they important? The oil weight or viscosity of and engine oil or lubricant is identified on the label with a number that will rate resistance to flow at 0 degrees F. This number is followed by the letter W (winter). The second number is the viscosity at vehicle operating temperature or more specifically 212 degrees F. If you live in a cold climate, you would want lower viscosity numbers and in reverse, if you lived in a warmer climate your vehicle would require higher viscosity numbers. Here in the Cary North Carolina area we experience mild four seasons which is right about what most vehicle manufacturers use to specify the oil viscosity in their engines. This makes it easier for us at Peak Auto to go by the “book”.
When synthetic oils were introduced in automotive maintenance, it gave the vehicle manufacturers a little more flexibility with the oil weights. Since synthetic oil is made of similar sized molecules it seems to pour more easily. Also, the synthetic oils seem to have better lubrication additive packages so that the oil can be “lighter” even running at higher temperatures. Therefore the vehicle manufacturers have decided to use very very thin or low viscosity oil in order to minimize drag of engine components while it is running therefore making engines more efficient and allowing your vehicle to get better fuel economy simply by using a thinner oil.
Don’t try this at home! It is not in our benefit to use thinner oils in our older vehicle to achieve better fuel economy. The savings is minimal and is done by car producers to meet strict government regulations, not to help you buy less gas. When the government mandates amount of emissions and fuel economy, auto manufacturers constantly look for ways to beat both apposing propositions while satisfying consumer demands for more power. Without worries of pollution, our SUV’s would not have to have Catalytic converters restricting the exhaust and therefore could get more power and better fuel economy. In the revers if fuel economy was not an issue, we could constantly add things to the engine to make it burn more clean. If consumers did not care about acceleration, then it would be easy to get fantastic gas mileage with little to no pollution. It would just take a very very long time to drive anywhere.