How To Choose The Best Motor Oil For Your Car

best motor oil to change

10w 40, 20w 50, 5w 20 … engine oil comes in a vast range of styles, thicknesses and blends, some would say that there is too much choice, but how do you know if you’ve picked the right one?

Speaking of choices, there must be more manufacturers than blends, so is one manufacturer better than the other? Would a ‘home brand’ work as well as what is perceived to be the best brand? Should you just pick any oil off the shelf and be done with it?

Well, certainly any engine oil is better than no engine oil, but you could be setting yourself up for a disaster if you choose wrongly.

The Job of Motor Oil

Before we get too far into blends, weights and additives, we need to understand a little more about the purpose of engine oil, and the rigours that it goes through as part of its job.

Obviously, first and foremost, engine oil is there to lubricate and reduce friction in metal parts, without it, you’d be quickly looking at premature wear, possible friction welding, overheating and damaged components – in other words, a pretty large repair bill.

But that’s the tip of the iceberg, engine oil does so much more.

Corrosion inhibitors help to prevent the build up of rust (the combustion process itself can create an atmosphere that aids the creation of corrosion), additives help to remove impurities and clean up deposits and foreign bodies within the engine, it also helps to cool the engine’s components and helps to seal the piston in the cylinder – it’s technical stuff.

It needs to be able to do all of this, cycling from cold to hot and back to cold for many thousands of miles, without breaking down or emulsifying.

Different Types

Generally speaking, there are three main types of motor oil (there are more specialist oils, but we’re looking at oils for the average motorist).

Mineral, Semi Synthetic and Full Synthetic.

At a push, it’s possible to mix oils, but it isn’t recommended; it can affect the running of the engine, possibly lead to burning oil and glazing the cylinder bores.

Mineral Oil

Mineral oil is generally used in older vehicles, it’s properties mean that it’s well suited to larger tolerances in the manufacturing of engines, and it isn’t quite as ‘slippy’ as a full synthetic blend.

Many manufacturers and performance engine builders use a mineral oil when breaking in (or running in) an engine – it allows the components to mate to each other, whereas a full synthetic oil would actually give too much protection, which would likely result in the cylinder bores ‘glazing’ up, leading to the engine burning oil (instead of a thin film coating the bore, it would allow the oil to sit in the combustion area, which then gets pushed out of the exhaust).

Mineral oil is generally the cheapest of motor oils, purely because it doesn’t offer the same protection and doesn’t have a lot of specialist additives, or at least not as many as the other blends.

Full Synthetic Oil

Considered to be the best motor oil, but that does depend on your need.

A full synthetic oil generally offers the most protection, but there are some things to be aware of; if you change your oil in your high mileage car from mineral or semi to a full synthetic, it’s more than likely that your engine will start burning oil – from the previously mentioned glazing of the bore.

With this in mind, a modern engine is designed to run on full synthetic – the manufacturing tolerances are closer, the processes allow for this kind of oil to be used without a problem, but it needs to be used from the start (after the running in period).

A full synthetic oil will last longer and offer more protection over the cheaper mineral oil, it won’t break down as quickly, although due to engine deposits, still needs regular replacement.

Semi Synthetic Oil

As you may gather from the name, this is a blend of the two; the theory being that it should offer a decent level of protection, without the expense of the full synthetic.

To a degree, that makes sense.

We would say that if you’re really stuck for adding oil in an emergency, without knowing exactly what you need, a semi synthetic blend would do the job without causing you too many issues – almost like the ‘one size, fits all’ variety.

Again, pricing sits between mineral and full synthetic, although if you’re stuck at the side of the road, that’s the least of your worries.

Grades & Weights

Grades & Weights

When manufacturers started producing motor oil, it was available as just one weight (or grade – basically the thickness of the oil). But today, there are huge amounts of different grades, some depend on engine type, some on environment (if you lived in a really hot or cold country for example) and the level of protection needed.

The Society of Automotive Engineers (SAE) introduced a simple grading system, for example – 10w 40 or 5w 30 and so on. The ‘W’ stands for winter – ie, cooler weather or another way of looking at it is cold start up – a 10w 40 would be thicker than 5w so in theory, would take longer to protect your engine on startup (although that’s a whole other post!).

The second number is a measurement at 100o Centigrade, again, the higher the number, the thicker it is.

When choosing an oil for your car, you need to factor in the protection needed, and the climate. Buying a 0w 20 will basically be like slippery water when it’s hot, and if you’re in a hot clime, that just exacerbates the problem.

You may also see ‘multigrade’ listed, this is just another way of saying the two different weights, rather than a single thickness, come hot or cold.

Your Choices

The easiest way of choosing the best motor oil for your car is to read the handbook, or have a look online – the designers, engineers and technicians that have put your car together have worked out the optimum for a wide range of differing conditions, in about 90% of the cases, they know best.

Of course, you could be travelling off somewhere with extreme temperatures in which case, understanding what could make for a better choice is a big decision. Rarely would we tell someone to ignore their manufacturers advice, above anything, you could invalidate a warranty if there’s a major mechanical malfunction, and the manufacturer could quite legally say that you’d caused the damage through incorrect oil choice.

However, with a little research and understanding, it’s quite possible that there is a better grade of oil for your specific needs, and avoiding simple problems (like fully synthetic oil in a high mileage vehicle), you should be fine with changing weights/grades.

Steven K. Galloway