Lubricants (motor oils) are liquids used for lubrication of various combustion engines. While the main function is to lubricate moving parts, motor oil also cleans, inhibits corrosion, improves sealing and cools the engine by carrying heat away from the moving parts. The majority of motor oils are derived from crude oil. Lubricants mostly consist of hydrocarbons: organic compounds consisting entirely of hydrogen and carbon.
Lubricants are categorised into mineral or synthetic motor oils depending on the production process technology. Mineral oils are produced by basic conversion technologies. They fulfill only minimum standards. Synthetic oils (low-viscosity lubricants) are produced in synthetic processes which significantly improves the characteristics of the product.
Advantages of synthetic motor oils
Synthetic motor oils have several advantages when compared to mineral motor oils. The main advantage is the high viscosity at a broad range of temperatures. This reduces fuel consumption significantly. According to the dena (German Energy Agency) and the ADAC (Allgemeiner Deutscher Automobil-Club), the following fuel savings can be achieved:
4 - 6 %
out of town
2 - 4 %
the most important advantages of synthetic motor oils are:
improved flow properties at low temperatures
low friction during cold starts of the engine
low wear and tear due to fast lubrication of the engine
the lubricant film is not cut in case of high temperatures
reduction of oil consumption due to higher vapour point
reduction of deposits in the motor
Classification of motor oils
The most common classification for motor oils is provided by the American Society of Automotive Engineers (SAE). The SAE designation for motor oils gives information about the viscosity of the oil at low and high temperatures. For multi-grade oils it includes two grade numbers. For example, SAE 10W-30 designates a common multi-grade oil.
The first number (e.g 10) associated with the W ('W' is for Winter) describes viscosity characteristics of the oil at low temperatures like in winter. The second number (e.g. 30) characterizes the viscosity of this multi-grade oil at 100°C (212°F) operating temperature.
As a basic rule it can be said that the lower the first number and the higher the second number, the better is the viscosity and thus fuel efficiency. For instance, a SAE 0W - 30 graded motor oil has very good viscosity properties.
The following oils are improved oils with lower fuel consumption characteristics:
SAE 0W - X and SAE 5W - X (X = 20 to 60)
For vehicles with diesel engines and particulate filter only low ash motor oils should be applied. They are indicated as "Low-SAPS-Oil" or "Low-Ash-Oil". They can be also indentified as ACEA classification C1, C2, C3 and C4.