Synthetic vs Conventional Oil – Myths Busted

We breakdown the myths surrounding synthetic and conventional oil, and whether you should use one or the other.

Oil: it's the lifeblood of your engine. There are many critical fluids that your car needs to run but engine oil is, arguably, the most important of those fluids. It's what lubricates the innards of your engine. Neglect it at your peril!

But when looking for engine oil on the shelves of your local auto store, you may notice something glaringly obvious: besides the multitude of manufacturers on offer, there are also two rather important categories: conventional oil (also known as mineral oil or non-synthetic oil), and synthetic (fully synthetic) oil.

What are the differences between them? Is one better than the other? And which should you use at your next oil change? Let's break it down below!

What’s the Deal Between the Two?

Let’s start with mineral oil. Mineral oil uses a base that is manufactured from crude oil. That base typically makes up 75-90% of the oil. Added to this are a plethora of additives. These include anti-corrosives, anti-foamers, viscosity index modifiers, and many more. This is the result of decades of research on how to best formulate an oil that keeps your engine running.

But, as you can see, conventional oil is far from just being oil straight from the ground. Synthetic oil, on the other hand, ditches this approach to the base oil, and instead uses synthetic fluids as the base. Synthetic oils still have additives added to them, but the base oil has gone through a process of chemical engineering that allows it to have more consistent properties for use in engines.

Does that Mean Synthetic Oils are Best?

In most cases, yes. Synthetic oils display better consistency when used in motor vehicle applications. Their particles are more uniform in size, and they can be engineered to be better at everything from temperature control to viscosity. And typically, synthetic oils can last longer too, potentially extending your engine oil change intervals.

However, there’s an argument to be made for conventional oil too. For one, they’re cheaper than synthetic oils. The price of conventional oil will save you a lot of money in the short run. And, if your car has been run for the majority of its life on conventional oil, you may be reluctant to make the switch to synthetic. There’s also a theory that engines that were designed in the past (such as on older classic and vintage cars) are better suited to mineral and conventionally-based oils. Although that can be contested.

Will Switching to Synthetic Oil Damage My Engine?

It’s highly unlikely that switching to synthetic oils would damage an engine. But, there are countless stories of those who’ve made the switch, noticing that their engines become noisier, and leaks become bigger.

There’s a simple explanation for such occurrences. If your engine has been used for some time, the chances are that, over time, the oil seals have developed cracks, and the internals have worn away somewhat. As conventional oil is not as viscous, nor does it flow as readily, such leaks are smaller and less noticeable (if at all). And, as the oil is thicker, it’s more forgiving to wear and tear.

When the switch to synthetic is made, you'll find that the new oil's viscosity is lower, meaning it'll move through passages quicker. That also means that those existing cracks will let more oil pass through—giving the illusion of increased or new leakage. The same goes for noise, as the new synthetic oil flows better, but is thinner, and fails to audibly mask the wear and tear that has always been present.

So, Which One Should I Use? 

If you have a brand-new car, the chances are that it is already is running on synthetic oil. You should continue to use synthetic, as although the short-term savings may present themselves attractively, you’ll save more in the long run with increased service intervals, and reduced wear and tear.

A car that has perhaps already clocked 150,000 miles on the other hands, is a different kettle of fish. Synthetic oil is better in almost every way, regardless of the application but, if you don’t want to preserve the engine, or suspect it’s been running on conventional oil throughout its life, then you may want to consider sticking to that conventional mineral oil.

If, however, your older car has had a good life, or even a newly-rebuilt engine, then you should, by all means, consider synthetic oil for the job. It won’t harm the engine, and the consistent properties of the oil will ensure it is better protected from things like wear and tear, temperature fluctuations, and of course the dreaded engine sludge.

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