Welcome to! This site is dedicated to giving you some basic facts about synthetic motor oils and other lubricants commonly used in today's cars and trucks.

What is synthetic oil?

The easiest way to define what synthetic oil is, is to define what it is NOT. Conventional motor oil as we have known it for the last 100 years or so is derived from crude oil that is taken from the earth with oil wells. Through a complex distillation process the crude oil is refined into many different liquids, or fractions, each having distinct characteristics. Some are very light and are used as fuel (gasoline, kerosene, diesel fuel), and some are heavier and are used as lubricants (motor oil, gear lube, grease). There are many molecular compounds present in crude oil and many of those compounds are still present in the refined product, detracting from the physical properties of that product. For instance, paraffinnic waxes are present in crude-based oil, but contribute nothing to the lubricative properties of the oil. Also, the size of the hydrocarbon molecules themselves are non-uniform in crude-based oils. Synthetic oil contains none of these contaminants and the hydrocarbon molecules are very uniform, giving the synthetic oil base better mechanical properties at extreme high and low temperature (see the sections below on physical properties). By contrast, synthetic oil is not distilled from crude oil. It is made through a chemical process known as the Fischer-Tropsch process, starting with raw materials like methane, carbon monoxide, and carbon dioxide. This process was developed by Germany in WWII, when that country's access to crude oil was very limited.

Grades of oil.

Motor oils are derived from base stocks. That is, a generic oil base is modified with additives to produce a lubricant with the desired properties. A base stock oil with no additives would not perform very well at all. Base stocks are classified by the American Petroleum Institute (API) and fall into one of five categories.

Physical properties

All oils behave differently at different temperatures. As temperatures drop, the hydrocarbon molecules in mineral oils start to line up and stick together. This causes the viscosity of the oil to increase, which makes it harder for it to lubricate an engine. At high temperatures, the opposite happens and the oil's viscosity decreases, making it less effective at protecting moving parts. Additives knows as Viscosity Improvers are added to combat this. Basically viscosity improvers are coiled molecules that shorten when cold, and lenthen when hot.
The short, cold molecules interfere with the hydrocarbons lining themselves up, and the longer hot molecules help things stick together better (at the molecular level) and keep things from getting too 'loose'. Unfortunately, viscosity improvers break down when exposed to heat and mechanical shearing, so oils that use a lot of viscosity improvers don't last very long.
This is where synthetics have an advantage. The branched-chain structure of synthetic oils naturally resist changes in viscosity with temperature. It's just the way they're made. Therefore, true synthetic oils often don't need any viscosity improvers at all! This is one reason synthetic oils last so much longer than non-synthetics. The physical property used to quantify an oil's resistance to viscosity change with temperature is known as the Viscosity Index (VI).
TBN is a measure of the oil's alkalinity. Alkalinity in an oil is important because the combustion process produces acids which can attack metals and other materials in an engine, increasing wear.
When oil is new the TBN is highest. Over time, TBN decreases until finally the oil reaches a point where it can not absorb any more acids and the acidity of the oil in the engine will start to rise. Most often, it is this depletion of TBN which signals that an oil is 'worn out' and due to be changed.
TBN is measured in milligrams of Potassium Hydroxide per gram (mg KOH/g). For automotive applications, TBN is around 7-10, while for diesels it is between 10 and 15 because diesels produce more acids and often go longer between oil changes. A synthetic oil that is formulated for long change intervals must have a high TBN.
The Pour Point is the lowest temperature at which the oil can still be poured out of a container. Non-synthetic oils can be so thick at low temperatures that they will not even pour out of the bottle! Synthetics generally retain pourability at any temperature you are likely to encounter in the physical world.
Flash point is the temperature at which the vapor of the oil will start to combust, but not continue to burn when mixed with air. Synthetics have much higher flash points than non-synthetics.
This is a test in which the oil is heated to a temperature of 250 degrees C for one hour, after which the percentage of weight lost by the oil is measured. This indicates the extent to which the lighter-weight fractions of the oil are volatilized and lost to the atmosphere.
An oil that volatilizes easily performs poorly because it quickly becomes thick and doesn't reach the far reaches of the engine we well. In extreme cases the oil turns into a sludge and catastrophic engine damage occurs. Noack Volatility is expressed as a percentage, so lower numbers are better. A good synthetic oil has volatility numbers under 10 percent or so. Conventional oils have Noack volatility numbers as high as 25 percent.
Shear stability is an expression of how well the oil stands up to mechanical shear loads. In an internal combustion engine, oil is subjected to extreme shear loads as parts slide past each other. Oils with poor shear stability will 'shear out' and lose viscosity. Synthetic oils have far superior shear stability compared to conventional oils.
Most oils contain detergent and dispersant additives to combat deposits and sludge build-up inside the engine. Diesel oils tend to have higher levels of detergents.
Most oils used in automotive and truck applications are Multi-grade oils. This is indicated by the familiar nomenclature like 10W-30 or 10W-40. The second number (30, 40, etc) is the nominal viscosity of the oil at 100 degrees C. Thus, a 10W-30 behaves the same as a straight 30 weight oil when it is hot. The first number is the Winter weight of the oil. It indicates how the oil behaves when cold. '10W' indicates than the oil behaves as a straight SAE 10 weight oil when cold. As previously noted, non-synthetic oils achieve this behavior with VI additives. Synthetics can easily achieve 5W or even 0W ratings with no viscosity improvers added. The bottom line is that synthetic oils pump better then non-synthetics when cold. In extremely cold climates a 0W-30 synthetic oil can be very beneficial.
More and more new engines use lighter oils, like 5W-20, to achieve higher fuel efficiency. Ford, Honda, and Toyota are using these oil weights in all their newer cars, and more will follow suit as fuel efficiency standards continue to be tightened. 0W-20 oils are also starting to hit the market. Most cars on the road, though, use something in the 5W-30 to 10W-40 range.
Yes, you can switch your car to synthetic oil at any time. Synthetic oil and conventional oil will mix without issues, so you don't have to worry about a little bit of old oil in the engine mixing with the synthetic and causing problems.
Conventional oils can leave a lot of deposits and sometimes even sludge inside an engine. Synthetic oil will gradually dissolve most of these deposits. An engine with severe sludge problems may need more specialized attention, such as engine flush treatments or even a rebuild. Normal cars that have had regular maintenance will have no issues, though.