Engine Oil 101

September 3rd, 2024

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Most of us are still driving vehicles with an internal combustion engine (ICE) as the main source of power for propelling our vehicle down the road.  In order for the ICE to run smoothly – in fact, to run at all – the engine needs oil to travel all around the engine’s working parts to lubricate them so that they can move freely within their confines without overheating from too much friction and to prevent the engine from imploding on itself, or exploding, whichever way you like to think of it. 

As well as lubricating the motor, oil helps to keep the ICE cool and retards any corrosion.  Most modern oils also contain a bit of detergent.  The detergent helps to flush any gunk that comes from wear and tear on the engine components and any older oil compounds that have formed through to the oil filter where these unwanted bits will be captured and removed altogether when the old oil filter is changed with a new one come next time the ICE oil gets changed as part of the vehicle’s regular servicing regime.

If you’re new to the world of car ownership, or new to changing your own oil rather than just taking down to the service centre and getting the friendly guys and gals to do it for you, you may be utterly bewildered by the wall of containers that confronts you at your nearest discount automotive supplies store.  What are all those different types and numbers?  Does it matter what sort of oil you get to put in your car? Yes, it does, so here’s what you need to know about the stuff. 

There are various types of ICE oil on the market as well as various brands of motor oil – as you probably noticed.  The various types of ICE oil have been designed for fulfilling a particular role or purpose, and they have also been designed for various ICE types.  It is important to know a bit about the oil additives used in the oil, the oil’s viscosity rating, and the oil’s classification code so that you can match the right oil for your particular vehicle’s ICE.

Oil additives

Oil additives help prevent corrosion of the metal parts inside the internal engine.  Oil additives also help cut down the friction of the moving parts and work to dissolve any impurities and sludge that may form over time.  The additives also prevent the oil from foaming up at high temperatures, as well as helping the oil pour better when the weather is colder and temperatures are lower. 

Consumer testing has reported no real difference in engine wear between vehicles that use synthetic oils and vehicles that use mineral oils.  The key is to change the oil according to the vehicle’s manufacture’s guidelines.  Some people even like to change the ICE oil before the guideline period.  If this is the case, there is no harm done to the engine at all; it’s just that servicing costs will be higher over time, but with the likely benefit of increasing the life of the ICE. 

Obviously synthetic oils have an even more controlled level of additives included in the oil’s make-up.  Some ICE designs are more prone to forming oil sludge over time, and there are those who like to use synthetic oils in order to ensure against any sludge building up inside their vehicle’s engine.  There are also some people who suggest that synthetic oils are better in cold climates because these oils don’t have as many waxy compounds to congest the oil when temperatures are cold.  An idea of viscosity helps us understand this better.

Viscosity

As soon as the ICE ignites into life, the engine’s parts are moving before the oil has the time to reach every single part of the internal working parts’ surfaces.  It’s when the engine is started cold that the most internal wear occurs.  Now, all ICE oil has a viscosity rating.  Viscosity determines the oil’s ability to flow in cold weather/temperatures and thus during cold starts.  The quicker the oil can get around the whole engine, the less wear and tear occurs.  In cold weather, oil thickens and becomes less able to flow through the engine.  It is also true that in hot weather, oil thins out.  Yes – when the weather is hot the oil thins out and pours quickly, it may become so thin that it can’t prevent friction.  It’s a bit of a Goldilocks situation – the oil can’t be too hot or too cold but just right.

There are two types of oil sold on the market.  One is known as single viscosity oil and the other multi-viscosity oil.  For many years now, almost every vehicle has been designed to run on multi-viscosity oil.  Vehicle manufacturers say what type of oil should be used for their vehicles, which is determined by the oil’s viscosity according to the temperature range that the vehicle is expected to function in the working period before the oil is changed (i.e., when the engine is due for its service).  The lower the number, the thinner the oil and more easily it flows.  An example of the numbers you’ll see on an oil container at your local automotive parts store is 10W-40.  The two numbers mean that it is a multi-viscosity oil that is effective over a range of temperatures.  The 10 refers to how the oil flows at low temperatures.  The 40 refers to how it flows at high temperatures.  The W means that the oil can be used in winter. 

The oil industry’s American Petroleum Institute (API) has an assigned symbol to certify that an oil meets the latest industry requirements, as well as a code for how well the oil protects the ICE against wear, corrosion, deposits, and oxidation.  The API symbol looks like a donut, and you should see this on any reputable brand’s oil container that you can buy from your local automotive parts store.  The donut symbol is used for both petrol and diesel ICEs and should be located on the outside of the oil container. 

The classification codes for vehicles with petrol engines started with SA in the early 1960s.  As the engines became more modern and demanding with their higher performance and fuel efficiency, the oil had also to get more refined and better able to lubricate at higher temperatures and within finer mechanical margins.  Thus, the codes progressed alphabetically from SB onwards.  At present, any oil coded SJ is no longer considered current, but you can use oils coded SM along with later codes in a vehicle of any age to make the engine run more smoothly and better overall.

So to recap: the lower the number after the W, the better the oil will work in cold weather; the higher the number after the W, the better the oil works in hot weather.  So 0W-20 oil will be great for a vehicle used in a place like Canada through its harsh winters, but it won’t be good for a vehicle located in central Outback Australia during the heat of summer.  A 30W-50 oil will be more suitable for hot Australian conditions.