The various numbers and labels on different car oil types can seem daunting. Fortunately, it isn’t as confusing as it seems once you understand it.

Perhaps the most confusing elements are the types of oil themselves and the numbers featured on the bottle (such as 5W-20). In this blog, we’ll give you the details of what these mean so that you can make an informed decision when choosing which car oil to use.

Engine oil weight explained

Oil weight doesn’t actually refer to the weight of a motor’s oil, but to the thickness or viscosity of it. This will usually be signified on the bottle by two numbers either side of a ‘W’, which stands for ‘Winter’.

What do the numbers on oil mean?

The numbers before and after the ‘W’ represent the viscosity of the oil at different temperatures. The first number is the thickness of the oil in lower temperatures, and the second is its thickness in higher temperatures. The higher the number, the thicker the oil.

When considering the viscosity of your oil in hotter temperatures, remember that this doesn’t just include your geographical environment, but also the heat of the engine itself. You generally want a higher viscosity in hotter temperatures as this will offer your engine better protection.

The owner’s manual of your car will usually include the recommended oil viscosity for your specific vehicle, but these don’t always take geographical heat into account. Therefore, your own judgement will always have to somewhat come into the decision when choosing engine oil.

Different car oil types

There are three different types of oil that you can use in your car. Each one has varying levels of quality and are best for use in different vehicles.

Before deciding on which oil you’re going to use, it’s worth doing some research into your car to see which type is recommended. That said, here is a run down of the main features of the different car oil types:

Conventional motor oil

Manufactured from refined crude oil, conventional oil is considered the ‘standard’ motor oil, and is also the most affordable. Conventional oil is better suited to older engines because it has a higher viscosity, therefore providing better protection for these mechanically inferior engines.

Conventional oil can last for up to 7,000 miles, but it’s recommended that you complete an oil change every 3,000-5,000 miles regardless. It tends to have a shelf life of about five years if you store it in a tightly sealed container away from direct sunlight.

Synthetic oil

Synthetic oil is, as the name suggests, is constructed from chemical compounds, with a base of refined and distilled crude oil. Although it can be more expensive, synthetic engine oil is much healthier for modern engines; particularly those fitted with turbochargers.

This is because it’s more chemically stable than other kinds of oil, and therefore less likely to oxidise or acidify, meaning it can protect your engine for longer. Fewer impurities and fewer deposits also mean that synthetic oil does not form sludge over time to the same extent as other oils.

Compared to the 7,000 mile limit on conventional oil, synthetic oil can last anywhere between 10,000-15,000 miles, which makes the extra cost feel a bit more justified. It does, however, have the same shelf life of around five years.

Synthetic blend oil

This kind of oil is a combination of synthetic and conventional oils, and as a result demonstrates the mid-point between the two in its list of features. Synthetic blend is a good oil option for use on older cars that you want to give the lower maintenance of synthetic oil.

Synthetic blend produces less carbon dioxide emissions than conventional oil and typically lasts up to 10,000 miles. It has a better viscosity than conventional oil, less product gets lost due to evaporation, and it can even improve your engine’s lifespan. However, it doesn’t do any of these things as well as fully synthetic oil.

Find a reliable vehicle today

Now that you know a little bit more about what goes into your car, it’s time to pick a reliable model for the daily drive.

Browse through thousands of listings of dependable used cars today at

adjust finance options

are you sure?

you’re about to remove this vehicle from your list. Are you sure this is what you wanted to do?


We'd like to keep you up-to-date!

We'd like to send you some occasional news, reviews and offers. We also have some trusted partners who'd like to do the same. Please choose from below, what you are comfortable with.

Email & SMS

Don't forget to create an account or sign in to save vehicles to your profile.