What Is The Best Oil To Use In My Car? Synthetic or Regular Oil?

Inside car engines there’s a bunch of moving parts that work together to generate the power to turn get you moving. These parts inevitably rub together, which creates heat and causes wear on the components.

And that’s where engine oil comes in.

Oil feeds into the engine and lubricates the components within the engine, which allows them to slide beside each other much more easily. The better lubricated the components are, the less friction they experience, the less heat they generate and the less they wear.

There are two types of oil available in the UK — synthetic and regular — and a fair bit of debate over which is best for your car. (Both oils break down over time and need to be replaced either during a service or in your own DIY car maintenance schedule.)

In this car maintenance blog, I'm putting both to the test to answer the debate once and for all.

What is regular oil?

Regular (also called conventional) oil uses base oils derived from gasoline blended with chemical additives to achieve manufacturer-specified levels of heat tolerance, breakdown resistance and viscosity.

Regular oil is relatively cheap and is usually recommended for low to moderate demand drivers.

What is synthetic oil?

Synthetic oil is created in a laboratory using precisely controlled ingredients. When blended with chemical additives, you get an oil with superior lubrication and engine protection properties. Synthetic oil also has better cleaning, heat tolerance and durability.

Is synthetic oil better?

Synthetic oil is more expensive than regular oil, which leads a lot of people to believe that it’s better. To see if that's the case, I’ve compared synthetic and regular oils across four categories — stability, breakdown, sludge and lubrication.

  • Stability: Synthetic oils are specially designed to stay thick and viscous both when the engine is operating and when it is inactive. This helps in two ways. First, thicker oils stick to engine parts better while the engine is running. Second, more viscous oils help avoid dry starts. A dry start is when a car has sat idle for an extended period of time and the oil has drained to the bottom of the engine. Obviously, this isn’t ideal as it leaves the upper engine components un-lubricated.
  • Breakdown: Synthetic oils are manufactured in the lab, which means there is much more homogeneity on a molecular level. (This is a fancy way of saying all the oil molecules are the same size.) This sameness helps synthetic oils flow more smoothly, experience less wear and degrade slower. This improved longevity means your engine is more likely to be protected in between services.
  • Sludge: This is related to the rate of breakdown as oil leave deposits in the engine (commonly referred to as sludge) when the oil breaks down. Because synthetic oils break down slower, they produce less sludge.
  • Lubrication: Both synthetic and regular oils are blended with additives to improve lubrication and keep engine parts running smoothly. Synthetic oils break down slower, decreasing the amount of sludge in the engine and improving long-term lubrication.