Some general oil info from millers oils
www.millersoils.co.uk/
What does the 'viscosity' of an oil mean?
Viscosity is a measure of the thickness of the oil. The viscosity of oil at low and high temperatures is measured on a scale determined by the Society of Automotive Engineers and given a number known as the SAE number. Therefore SAE 30 oil will be thinner than SAE 40.
What is a multigrade oil?
Before the 1960s, all oils were monograde. Multigrade oils were developed have a designation in the format 20w50. Mulitgrade oil was made possible by the use of polymers, that expand as they get hotter. Therefore a multigrade oil can have the viscosity of an SAE20 when it is cold and the viscosity of an SAE50 when hot. This removes the necessity to change from thin oil in the winter to thicker oil in the summer, and maintains the best protection for the engine over a wide range of running temperatures. The 20w number is the cold viscosity and the 50 number is the viscosity at 100°C.
What is the difference between mineral oil and fully synthetic oil?
Both types are made from crude oil. Mineral oil is obtained directly from the refining process, whereas synthetic oils are altered by chemical processing which improves its chemical structure. Synthetic oils have better performance than mineral oils at all temperatures, and are more durable. They are more expensive but are higher quality, offer higher performance and longer life.
What are the specific characteristics and advantages of synthetic oils?
The advantages of synthetic oils are:
• Better flow at low temperatures enabling thinner oils to be manufactured. Thinner oils are required by modern engine designers to
help reduce fuel consumption and emissions.
• Higher film strength which gives better protection thereby reducing wear.
• More stable and less volatile at high temperatures, reducing oil consumption.
The interesting 'Race Technology Magazine – Synthetic Oil' article explains the advantages in more detail
What is a semi synthetic oil?
As the name suggests, a semi synthetic is a blend of mineral and synthetic base oils. The performance, price, quality and durability is between that of a mineral oil and fully synthetic oil. Lower quality semi synthetic oils have very little fully synthetic content and will not last as well as good quality examples.