NOBODY ever paid much attention to engine oil until a 1970s advertising campaign declared that 'oils ain’t oils'.
People who owned cars were suddenly interested and started caring about that gloopy, honey-coloured stuff that was tipped into their car’s engine from time to time.
But even though we knew oils were apparently not oils, not too many of us understood what made one different to another and, truth to tell, probably still don’t really know much about the stuff.
So while a story about engine oil is not the most riveting thing anyone will read today it is important to know, especially as using the wrong gloopy, honey-coloured stuff might not only damage your engine but also, in some instances, void your new car warranty.
Brought down to its basics, oil is a lubricant used to stop metal engine surfaces from wearing as they rub against each other by putting a thin film between them.
At a more complex level, the oil also reduces heat build-up and reduces dirt deposits by keeping the particles in suspension and even reduces corrosion-causing acid build-up.
The first thing to understand is viscosity, which is a measure of a fluid’s thickness or flow resistance.
Oil viscosity needs to suit the ambient temperature range in which the vehicle operates. If it is too thick when the engine is cold it will not flow easily, leading to wear on start-up and early running. If it is too thin it cannot give the high running temperature needed to provide the right level of engine protection.
After viscosity we need to look at the oil’s grading.
Most general purpose oils are known as ‘multigrade’, a lubricant blend which minimises viscosity fluctuation across temperature variations.
Multigrade oils are identified by two numbers on the label, such as ‘10W-40’, which show they can maintain engine protection across low and high temperature ranges.
The first number represents the lubricant’s low temperature viscosity and gives an indication of how the oil flows in winter. The lower the first number, the thinner the oil at low temperatures. And the ‘W’ shown on the label? It stands for ‘Winter’.
The second number shows the oil's high temperature viscosity. The higher the number, the thicker the oil stays at high temperatures. Using the correct viscosity, as recommended by the owner’s manual, increases engine performance while reducing wear and increasing fuel efficiency.
Also consider there are two types of engine oil available, mineral and synthetic.
Mineral oils and Synthetic oils
Both are blended with detergents to keep the engine clean and neutralise corrosive acids that form when fuel is burned, dispersants to remove soot and sludge, anti-wear additives which place a chemical layer between the moving parts, antioxidants which delay the oil’s natural degradation, friction modifiers to reduce drag between the moving parts and anti-rust additives to reduce stop engine corrosion.
Because of this, fully synthetic oils have better low- and high-temperature properties than normal mineral oils. They also have better start-up flow qualities and heat resistance in high temperature conditions. Synthetic oils also tend to be more expensive.
If your car tells you that you need to top up your engine oil (because who makes dipsticks anymore), the important thing to remember is to use the oil recommended by the car manufacturer and if you are considering changing from a mineral to a synthetic oil (or vice-versa) then consult your car’s handbook or a service technician.
Because oils really ain’t oils.
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