OIL VISCOSITY & LABELLING
What is oil viscosity?
Viscosity is an important criterion of any lubricating oil. It is a measure of a fluid’s thickness or resistance to flow. For example, honey is thick and water is thin, so honey has a higher viscosity than water. Oil viscosity needs to suit the right ambient temperatures. If it’s too thick when the engine is cold, it won’t move around the engine. And if it becomes too thin when the engine is hot, it won’t give the right protection to the engine parts.
Optimising an oil’s viscosity, or thickness, helps maximize energy efficiency while avoiding component wear.
Viscosity modifiers increase the viscosity of your oil at high temperature but have little effect on low-temperature viscosity. These enable your oil to flow properly when cold and also to remain thick enough to protect your engine components at high temperatures.
Lower-viscosity grades of oil such as TOTAL Quartz 9000 5W30, make it easier for your engine to start from cold because they present less resistance to moving parts and hence take less power from your engine. This also means that you get enhanced fuel economy.
What do the oil numbers mean?
Multi-grade oils are those oils that have two numbers on the grade, indicating that the oil is able to maintain engine performance in high and low temperatures. A multi-grade lubricant minimizes viscosity differences under temperature variations.
The first number on a multi-grade oil is normally followed by a W, which stands for winter. This number represents the lubricant’s viscosity under lower temperatures, giving an indication of how the oil will flow in the winter. The lower the first number, the thinner it is at low temperatures. The lower the viscosity grade, the lower the temperature the oil can pass. For example, if an oil passes at the specifications for 10W and 5W, but fails for 0W, then that oil must be labelled as an SAE 5W. That oil cannot be labelled as either 0W or 10W.
The second number, which appears after the W, represents the oil's viscosity under high temperatures. The higher the number, the thicker the oil will stay at high temperatures. Using the correct viscosity for your engine increases engine performance, reduces engine wear and increases fuel efficiency.
So as an example a multigrade 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature. This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear.
In addition, synthetic oils usually have better low and high temperature properties than normal mineral oils. This maintains protection while allowing better fuel economy and cold starting.
Continue reading the next update to find out additional differences with Mineral & Synthetic Oils.