Engine oil is the lifeblood of an internal combustion engine, without a good supply of quality oil an engine will destroy itself in seconds.
The engine oil’s primary job is to lubricate the moving parts of an engine. It does this by forming a thin film over the machined surfaces of engine components, to prevent them form actually touching each other, and therefore wearing at each other.
Lubrication is the engine oil’s main job, but it also has several other vitally important roles. It prevents corrosion of the metals it coats, it takes heat away from the combustion chambers aiding the cooling system, and it also removes any potentially damaging dirt particles from the engine by transmitting them to the oil filter.
As the engine oil reduces the friction between engine components, it can actually affect fuel economy and even the engine’s power output iuf the correct oil is used.
What are the different types of engine oil?
There are three major types of engine oil; mineral, synthetic, and semi-synthetic.
Mineral oil is a natural petroleum-based product, refined from crude oil. Synthetic oil is completely man-made, and designed with specific properties to suit specific engines or conditions.
Semi-Synthetic oil is a mix of the two, which can be created using varying proportions of both mineral and synthetic oils.
Most cars on the road today will use at least semi-synthetic oil, with more modern engines designed to make use of fully-synthetic oils.
Fully-synthetic is the preferred choice for most applications as it stable to much higher temperatures and pressures, but the downside is that it is much more expensive. Also, some older engines are better suited to run on mineral oils, as some of the chemicals in the synthetic oils can actually have adverse effects on older gaskets and seals.
What are the different grades of oil?
Any oil, mineral or synthetic, will be given a grade. In fact it will have two figures on the bottle – for example, 0w-40, 5w-40, or 10w-50. But what do these figures actually mean?
Well, they indicate the oil’s viscosity. This is basically a measure to show how easily the oil will flow – the higher the number, the thicker the oil. The first number is followed by a ‘w’ (for ‘winter’) and shows the oil’s viscosity rating when it is cold.
The second number then shows the oil’s viscosity when the engine, and therefore oil, is up to operating temperature. Having these two operating grades is why such engine oils are referred to as multigrade oils.
You might think that the best choice of oil would be the one with the highest differential between these two grades; a 0w-60 for example, with a low cold temperature rating that allows the oil to reach all the moving parts quickly when cold, and a high operating temperature rating meaning the oil remains viscous and can protect the engine at high temperatures.
But this is not necessarily the case. The engine oil used will need to suit that particular engine. For example 0w might be too thin to protect the engine at start-up, or 60-grade may be too thick for the engine’s small oil galleries, even at high temperatures.
Therefore, it’s always best to stick to the manufacturer’s engine oil recommendations. They would have spent a lot of time and money researching which oil works best in that particular engine, so it’s wise to follow their advice.
