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The best oil for your car was once a simple matter: Buy a good quality brand and change the oil regularly.
These days, it’s a lot more complicated with far more diversity in engines, fuels and grades of oil.
But there are still some ground rules that can keep your car running sweetly, and maybe even save you some money.
And it’s easy to research.
Modern engines have some very different requirements when it comes to oil these days, so you need to get it right. In fact, passenger vehicle motor oil is a huge branch of automotive science.
The absolute best way to make the right choice is to consult the owner’s handbook in your car’s glovebox.
Inside that document will be all the information you need to know when it comes to what oil to use.
If the handbook is missing, you can call a dealership and ask the service department for its recommendation.
Even visiting a parts store can reveal the answers. The oil aisle should have a book or chart listing the vast majority of makes and models and the oil that’s right for them.
If you can’t get to a store, you’ll find some oil companies have online databases, or even phone hotlines where you can search for your make and model and find the answers.
Simply asking `what oil is best for my car’, or `what oil does my car take’ will usually be enough to point you in the right direction.
At a very basic level, the oil-filler cap on top of your engine will sometimes list the viscosity rating of the oil it requires. (We’ll get to viscosity in a minute.)
Sometimes the manufacturer will apply a small decal somewhere under the bonnet that lists the brand and grade of oil that is appropriate for that car. Take a few moments to have a look around under there.
Friction is the one-word answer here: The metal parts in an engine rub against each other at incredibly high speed and that creates friction which in turn creates heat.
Rub your hands together quickly and you’ll experience this very science.
If it wasn’t for oil reducing that friction, a car engine would melt within minutes of being started.
Basically, it wears out.
As time and kilometres pass, the hard-working oil becomes less able to reduce friction.
That’s why carmakers specify the correct time interval or kilometres-travelled figure to let you know it’s time to change the oil before any damage can be done.
Which is also when most people suddenly start asking questions about oil.
The other reason to buy oil is to top up the level in the car’s engine.
Some (most, actually) cars consume some oil between oil changes and, if it’s enough, you need to top up the level.
Checking the dipstick under the bonnet is the traditional way to do this, but some modern cars have electronic measuring systems and will even alert you if the level has fallen too far.
Because modern engines use some pretty exotic metals and much closer tolerances (everything is a tighter fit, further increasing friction), modern oils are much more complicated in terms of their chemistry.
They are most certainly not simply refined crude oil; they have complex additive packages to make them better at lubrication.
Even then, it’s not that simple, and high-revving, multi-valve engines usually need a thinner oil to prevent damage on start-up, while older engine designs often require a thicker oil to maintain correct oil pressure.
Either way, there’s no one-size-fits-all oil and getting it wrong can wreck an engine, which is why this subject is so important.
You can learn a it about an oil from the label on the container, too.
Make sure you use an oil with the correct API (American Petroleum Institute) rating as this will ensure the oil is at least as modern as the engine it’s going into and has been okayed by the car’s manufacturer for that vehicle.
The current API rating is SN, and these ratings go backwards through the alphabet as you wind back the clock.
For instance, an engine in an older car might be perfectly happy with an oil with an API rating of SG. But a brand-new car with a modern engine design will not.
The other important letters and numbers are the oil’s viscosity; basically, how runny it is.
Low-viscosity oils flow faster and lubricates faster when you hit the ignition key.
But in hot climates like ours, it’s possible that you can go too low and finish up with oil that isn’t `sticky’ (viscous) enough to lubricate properly.
As an example, a lot of modern engines will use a 5W30 oil. The 5W relates to the oil’s viscosity in cold conditions, while the 30 represents its viscosity at normal operating temperatures.
On that basis, a 10W40 is thicker both in hot and cold conditions, while a 0W20 oil will flow faster on start-up but may not give you the protection you need in hot conditions.
And don’t forget to specify what fuel your car runs on as this has a big effect on the correct oil too; diesel engine oil is far from the same as petrol engine oil and contains a lot of detergent just for starters.
The other big debate is over synthetic versus mineral oil.
In reality, all engine oils start out as crude oil from the ground, and while mineral oil is refined to make it suitable for engines, that’s about it.
Synthetic oil, meanwhile, is more expensive because it’s further refined and distilled to `smooth it out’ at a molecular level, and is then treated to a more sophisticated range of additives to stretch its viscosity range.
Just some of those additives include friction modifiers, antioxidants and anti-foaming agents.
Without these additives, synthetic oil would not be able to offer the range of viscosities in one product.
Somewhere in the middle of that is semi-synthetic oil which, as the name suggests is a mixture of the other two and is a neat way to get a relatively high-tech oil at a mid-range price.