Using the correct viscosity oil is important because higher viscosity oils have greater resistance to the moving parts of the engine, and, therefore use more gas. Clean oil also contributes to better gas mileage. It is usually recommended that engine oil be changed every five to ten thousand kilometers.
Conventional motor oils are made from crude oil which has been pumped from the ground and then processed in a refinery to create a base oil. Additives are then mixed into the base oil to change the viscosity, protection properties and heat break down levels of the oil. The unstable molecules in conventional oil can easily vaporize or oxidize in extreme heat. Conventional oils contain small amounts of sulphur, wax, and asphaltic material that can promote detonation, as well as varnish and sludge build-up. Conventional oil is recommended for older vehicles and is the least expensive.
semi-synthetic oils are an alternative to buying pure synthetic oil. These combine a certain quantity of synthetic base oil with a conventional base oil in order to provide a high quality oil which can be used to gain some of the protection benefits of a fully synthetic for slightly older vehicles. However, semi-synthetic engine oils do not typically include all the synthetic oil’s advanced additives.
Because synthetic oil’s molecules are much more consistent in size and shape, they are better able to withstand extreme engine temperatures. Mobil 1 synthetic is said to be capable of protecting engines “at well over 400 degrees F”.
Because synthetic oil is chemically produced, there are no contaminants in the oil. With no wax, synthetics will flow at much lower temperatures than conventional oils. In fact, synthetic oils are now available with viscosity ratings as low as 0W-20, as in Mobil 1’s Tri-Synthetic blend. These oils flow more than seven times faster than conventional 5W-20 motor oils during initial start-up, yet at normal operating temperatures act like a regular Grade 20 oil.