SCIENCE CORNER FAQ
Learn about conventional vs synthetic oil, grades, viscosity, alkalinity, TBN, flash point, shear stability, multi weight, and the best synthetic oil qualities.
What is Synthetic Oil?
Motor oil is basically derived from crude oil that is taken from the earth. Through distillation is refined into liquids. Some are light and become fuels such as gasoline or diesel fuel. Others are heavier and are used lubricants. There are various molecular compounds present in crude oil and many are present in the refined products, sometimes negatively affecting the physical properties of such products.
E.G. Waxes are present in crude-based oil but contribute nothing to the lubricating ability of oil which is true of the hydrocarbon molecules also found in crude. Synthetic oil does not contain such contaminants. In synthetic motor oil, hydrocarbon molecules are uniform, giving it exceptional properties consistent at high and low engine temperatures.
How Many Grades of Oil are There?
Engine Oil is derived from base stocks. The base is modified with additives to produce lubricants with desired properties. A base stock oil with no additives will not perform well. Base stocks are classified by the American Petroleum Institute (API) and fall into five categories.
GROUP I AND GROUP II – mineral oils commonly known as “conventional oils” which are derived from processed crude oil.
GROUP III – this is a more highly refined mineral oil made through a process called hydrocracking. In North America this group is considered a synthetic oil due to the process involved.
GROUP IV-this is synthetic oil, known as Polyalphaolefin (PAO).
GROUP V-this is synthetic stock oil other than PAO’S and include esters and other compounds.
What is the Significance of the Viscosity Index?
Engine Oils perform differently and often have different viscosity at different temperatures. As oil temperatures drop the molecules in mineral oils begin to stick together. This causes the viscosity of the oil to increase – thicken. At high engine temperatures oil’s viscosity decreases making it less effective as a lubricant. Therefore, additives known as viscosity improvers are often added to combat this. Unfortunately, viscosity improvers can break down when exposed to heat and mechanical shearing, so engine oil that uses a lot of viscosity improvers won’t last a long time. Therefore, synthetic oil makes sense.
The structure of synthetic oil resists changes in viscosity with temperature changes and does not require viscosity improvers. This is one reason synthetic oil lasts so much longer than non-synthetics. The physical property method used universally to quantify an oil’s resistance to viscosity change with temperature is the Viscosity Index.
The higher the Viscosity index of any motor oil the more resistant to viscosity change the oil is. Onguard engine Oil is formulated at the top level of the Viscosity Index which is level five (#5.)
What does an oil’s TBN relate to?
TBN stands for “Total Base Number”. TBN is a measure of the oil’s alkalinity. Alkalinity in oil is important because the fuel combustion process produces acids which can attack metals and other materials in an engine, increasing internal component wear. Synthetic oils, to be formulated for long, between change intervals, must have a high TBN.
What is meant by an oil’s flash point?
Flash point is the temperature at which the vapor of the oil will start to combust but will not continue to burn when mixed with air.
Synthetic oil has a much higher flash point than non-synthetic.
What is Shear Stability?
Shear stability is a determination of how well the oil will stand up to mechanical shear loading. In an internal combustion engine, all oil is subjected to shear loads as parts slide past each other. Motor Oil with poor shear stability will “shear out” lose viscosity. Synthetic oils have far superior shear loading stability compared to most conventional oils.
Why does engine oil have multi weights?
In modern times, oils used in vehicles are multi-graded oils. Let’s take 10 W 30 and use it for an example. The “W” stands for “winter”. That is what “weight” or viscosity the oil is when it is cold. The second number 30 is the viscosity of the oil at 100 degrees C. Therefore, a 10 W 30 motor oil behaves the same as straight 30 weight when it is hot.
Non-Synthetic oils achieve this behavior with additives. Synthetic oil can achieve 5 Weight or even 0 Weight ratings.