Why ‘Thinner’ Oil Offers More Cost-Effective Lubrication

Oil in a lab for thin oil blog

Particularly in the Passenger Car, LCV, and Commercial Vehicle markets, there is a trend for thinner oil, a reduced oil viscocity. We asked Mark Crossley, a member of our technical support team, to explain

Firstly, what is viscosity and why is it important?

Viscosity is the “thickness” of a fluid, and is an important characteristic of a lubricant. The viscosity determines the film thickness and film strength of an oil. These are critical for reducing friction and keeping metal surfaces apart.

So the thicker the oil, the better the lubricant?

No – that’s actually a common misconception. The oil needs to be right for the application.

High viscosity or “thicker” oil is not necessarily better. If the viscosity is too high it can cause excessive energy consumption, heat generation, and poor start-up lubrication.

If the viscosity is too low, there will be oil film failure and insufficient lubrication, which then leads to friction and wear as well as sensitivity to particle contamination.

It’s important to select the right viscosity oil for your vehicle, which depends on how your engine or gearbox is designed, and what the application is. We always advise customers to check the OEM specification or use our Which Oil? selector to find the right product for their vehicle.

But is it true that oils are becoming “thinner”?

Yes, the viscosity of the oils that meet the latest vehicle specification are in general lower than they were several years ago. This is due to an improvement in additive technology, and a drive for increased fuel efficiency. 

Modern additive technology means that we can formulate with lower viscosity base oils, as the additives can provide additional lubricity required to protect the engine components.

This allows us to use lower viscosity oils, which take less energy to pump around the engine. Think about the energy it would take you to squeeze a bottle of water vs. syrup. This then translates to improved fuel economy and savings for customers.

Typically, moving from a 10w40 engine oil to a 5w30 would show a fuel economy improvement of around 1-2%.

So what sort of cost-saving are we looking at for a typical truck?

Even taking into account the cost difference between a 10w40 oil and a more expensive 5w30 oil. This is because of the large number of miles covered each year and the cost of fuel. The average annual saving per truck is over £1000.

Thanks, Mark.

For more information on this topic, contact technical@millersoils.co.uk