With such a vast selection of engine oils available today, how can garages be sure they are using the correct type, and what happens if they use the wrong one?
In the past, the range of engine oils was much more limited, with a 10W-40 grade being suitable for a raft of different vehicles.
Bob Wood, Technical Engineer at Total Lubricants, explained: “The reason there are so many oils today is due to a combination of factors, including advancements in engine technology, tightening emissions regulations and consumer demand. The engines in modern cars are more complicated than ever before and the tolerances are lower, so gone are the days when there were just a couple of grades to choose from.”
Vehicle and lubricant manufacturers continually strive to improve the fuel economy of cars by reducing the viscosity of engine and transmission oils. However, although a thinner oil flows more freely and requires less energy for it to be pumped around the engine, lubricant manufacturers must also find ways to mitigate wear within the engine.
Bob explained, “Using the wrong viscosity oil may lead to increased friction, resulting in excessive wear on engine components, so state-of-the-art additives to balance any loss of wear protection due to the lower viscosity are added to the base oil.”
Synthetic and mineral
Traditionally, mineral oils were predominantly used, and although these are still used to some extent today, they are being replaced by synthetic oils. Although they are more expensive, synthetic oils are thinner, meaning they cope better with high temperatures, flow more effectively in colder temperatures, and ultimately offer better engine protection and performance.
The viscosity (or thickness) of an oil indicates how it will flow at given temperatures. The Society of Automotive Engineers (SAE) developed a scale for motor and transmission oil viscosity. The ‘W’ on the code on the label stands for ‘winter’ and the number preceding it indicates the oil’s flow at different low temperatures; 0W-35°C, 5W-30°C, 10W-25°C. The lower the number, the more effectively it will perform in cold weather. The second number, after the ‘W’, indicates the oil’s viscosity when measured at 100°C. This number represents the oil’s resistance to thinning at high temperatures.
Testing and specifications
Viscosity is one way of assessing how well a particular oil will protect an engine, but manufacturers also carry out various tests during oil production to ensure the oil contains the correct additives at the correct concentrations to give the desired performance. These are then endorsed, for example, in Europe, by the European Automobile Manufacturers Association (ACEA), an organisation which defines the specific requirements needed for various types of engine, through the ACEA oil sequences, with each one being classified with a letter followed by a number to identify the class and category of the oil.
Bob concluded, “It is very important that the correct oil for a particular car is used, both in terms of the viscosity and also the performance needed – using the wrong oil could damage the engine and the exhaust system. Most lubricant manufacturers have an online service which can identify the correct oil for a particular vehicle, such as Total’s Lub Advisor UK. The information can also be found in the vehicle handbook or on the manufacturer’s website.”
