Engines require motor oil to keep them running smoothly. But when you go to the store, how do you select the best motor oil? Do the numbers actually mean anything?
In a short answer…yes. The motor oil numbers do have a meaning. The Society of Automotive Engineers (SAE) Viscosity rating has created a system to categorize oils. The oil’s resistance to flow is called viscosity. Thicker oil has a higher viscosity number. Thinner oil has a lower viscosity number.
But wait…there are two numbers! Each number represents a different temperature. The first number describes the oil viscosity at low temperatures (engine not running) and the second refers to the viscosity at normal engine operating temperatures.
So what about the “W”? The “W” means that the oil has been tested at a colder temperature. The approximate temperature of a running engine is 210º F, which is what the standard oil (without the “W”) has been tested at.
Okay, so now you know what it means…but what difference does it make? Vehicle engines may need different oil thicknesses when starting up. The “W” usually indicates better oil for colder temperatures.
For example, a 5W-30 motor oil will warm up quicker in colder weather which will reduce engine wear. Once the motor is running at a normal temperature, the oil will become thicker and be similar to SAE 30 motor oil.
Let’s look at some numbers. The “5W” in a 5W-30 will represent the thinner oil, able to work effectively in the winter when starting up your vehicle. The “30” is what the oil will be once your engine is running at a normal temperature. Oil with a “30” is well-suited for most cars, unless you are driving a race car or a vehicle with extra hot temperatures in your engine. For advanced temperature protection, you will want to go with a higher second number, like “50”.
See? Motor oil numbers are not as difficult as they seem. There are several resources to increase your knowledge of motor oil numbers. However, the best resource is always going to be your owner’s manual, which will explain exactly which oil numbers your car needs.