Can you mix engine oils?

It’s essential to protect your car engine by ensuring your engine oil is topped up and your oil filter is working correctly to remove debris and contaminants. However, if you’ve ever wondered whether it’s ok to mix engine oils, you’ve come to the right place!

Engine oils each have their own viscosity, which is defined by how easily it pours at certain temperatures. It may seem fine to mix two different branded engine oils together, providing they are the same viscosity, but this isn’t necessarily the case.

Keep reading to discover what happens when you mix engine oils together and why you should avoid it.

Engine oils are usually split into three types: mineral, semi-synthetic and synthetic.

• Mineral oil contains a high viscosity level, meaning it deteriorates more quickly when exposed to high temperatures.
• Semi-synthetic oil contains more additives than mineral oil, is usually cheaper than synthetic oil and has a higher heat resistance.
• Synthetic oil, often labelled as ‘fully synthetic oil’, retains its properties even during very high temperatures. How long synthetic oil lasts will depend on the brand you are using but it will last longer than other oil types.

You can find the correct type of engine oil for your vehicle by looking in your vehicle handbook. You can also use our online engine oil look-up tool. Simply enter your vehicle registration number and the relevant engine oils for your vehicle will appear.

When it’s time to change your oil, it’s also important to replace your oil filter as this can clog up over time.

While mixing certain engine oils may not necessarily cause any harm to your engine (i.e. they consist of the same formula), it’s not recommended that you mix different oil types and grades due to potentially impacting the properties, which could affect your engine.

While all engine oils are manufactured to an SAE (Society of Automotive Engineers) standard, it is not recommended to mix different brands of engine oils, even if they are the same viscosity as each brand uses their own formula. If you’re looking to use a new brand of engine oil, this is ok providing that the old oil is completely drained . We recommend using an engine flush each time you have an oil change to remove any sludge and contaminants.

The letters and numbers for different oils cans be confusing. The low number at the beginning, refers to the viscosity of the oil at low temperatures, the second number refers to the viscosity at high temperatures, while the W stands for ‘winter’. 5W-30, for example, is more effective during colder temperatures as the oil is thinner.

It is not recommended that you mix 5W-30 and 10W-30 oil, given that they are formulated to be more effective at different temperatures. If you need to top up your oil in an emergency, it’s best to stick to oil from the same brand to reduce any potential engine damage.

When you’re next able to, completely drain your oil and replace it with the correct oil type to prevent any potential damage further down the line.

Using the wrong type of engine oil for your vehicle can lead to engine damage and even engine failure. It can wear down the metal parts, create worrying noises and your car may also struggle to start. Modern car engines can contain wet belts, which must have both the correct engine oil and be replaced at the manufacturer recommended interval, so it’s crucial to get it right. If you have put the wrong oil in your vehicle, speak to your local Halfords garage as soon as possible.

At Halfords, we stock a range of engine oils for all vehicles including top brands like Petronas to our own Halfords brand. Enter your vehicle registration now to find the right engine oil for you.

To discover more about engine oil, check out our engine oil buyer’s guide or our article on how to check your engine oil.

If you find yourself in need of a new oil filter, you can find the right one for you by entering your vehicle registration online. With free next working day delivery on all car parts orders, getting the right part has never been quicker and simpler.