Why low viscosity engine oil is recommended in modern engines?

Article by: Dr Trisonic. Nov 2019.

This morning, a customer submitted an enquiry to TriSonic website, asking why low viscosity oil is used in the modern engines.

As the governments around the world legislate stricter fuel-economy standard, the car manufacturers increasingly incorporate engines that use low-viscosity engine oils into their cars to help them meet such requirements.

Engine oil is a balanced complex product that is integral to the engine’s performance.  It is as important a part of the vehicle’s engineering as the pistons and valve gear.  The car manufacturers tend to use lower-viscosity oils in their latest engines.  This reduces internal friction since the lower viscosity oil flows more easily than higher-viscosity oils, which improves fuel economy.  Using low viscosity engine oils is one of the easy cost-effective option to achieve the overall fuel economy standard.  

Using low-viscosity oil was problematic in the past due to the greater clearance between piston and cylinder wall: thinner (low-viscosity) oil tended to slip through the wider gap and was burnt off together with the gasoline fuel.  This resulted in greater engine oil consumption and thus the engine needed frequent engine oil top up.

However, today’s engines are built with much tighter tolerances than their predecessors; the clearance between the crankshaft journal and the main bearing are now tighter.  This is intentionally done to allow the use of low viscosity engine oil, like SAE 0W-20 and even SAE 0W-16.  Low viscosity oil is used today because the oil is able to flow faster and fill the tiny clearances between parts, leading to a durable, consistent lubricating film, thus better engine wear protection.

For these advanced engines, using thicker engine oils like SAE 15W-40 and SAE 20W-50 in would lead to wasted energy pumping the thicker engine oil, thus reducing fuel economy.  In addition, since thicker oils possess lower heat transfer capability, operating temperatures will increase, leading to accelerated chemical break down and the production of harmful sludge and deposits resulting in shorter engine life.

As mentioned in my previous articles, to avoid any problems with engine protection, my advice would be to use the viscosity recommended in your car owner’s manual, which denote the appropriate SAE standards (for example SAE 5W-30 or SAE 10W-40). 

It is more important to choose a trusted engine oil with API approvals such as TriSonic™ UltiMach™ 100SYN FE 5W-30 to ensure optimal performance and reduce problems.  Such engine oil has been tested by the American Petroleum Institute (API) (indicated by the ILSAC starburst and API doughnut) and passes the rigorous standards required of an engine oil that ensure reliable and efficient performance.   Choosing the right engine oil is important, and it can mean the difference between years of smooth engine running or frequent engine problems.