quality and viscosity

Modern oils are often marketed as superior to older formulations, leading some to think they can be used in any engine without constraint. Yet many confuse oil grade with viscosity. The two terms describe different properties, and recognizing their distinction is essential for proper engine care.

Today’s most advanced motor oils carry SP grade designations, replacing older SM or SN groups. This shift centers on specification levels rather than the SAE viscosity rating. Low-viscosity oils such as 0W-20 are advised for many contemporary engines, but that does not mean they should be poured into every older engine.

Low-viscosity oils feel runnier than traditional lubricants, which can be puzzling for drivers. How can a thinner oil protect an engine? Manufacturers of modern engines often promote low-viscosity oils for efficiency and performance. For engines designed long ago, however, these oils may not be suitable.

How do you recognize low viscosity oil?

Most people rely on the SAE viscosity rating. The numbers after the W indicate how oil viscosity changes with engine temperature, roughly aligned with the temperature at which the engine operates. Generally, higher numbers correlate with higher viscosity.

Beyond SAE, there is the HTHS parameter, describing high-temperature viscosity. This measures dynamic viscosity at high temperatures, not the simple kinematic value. It gauges resistance to layers sliding past one another inside the oil film, indicating energy efficiency and bearing protection.

HTHS is not printed on consumer containers; instead, it is embedded in the engine oil specification itself. The relationship between HTHS and SAE specifications is shown by how different xW grades map to specific high-temperature performance and film strength, as demonstrated in the following relationships:

Which oil protects the engine better?

Lower HTHS means less friction and better energy efficiency, which can translate to lower emissions and reduced fuel use. Higher HTHS provides a thicker oil film, but does not automatically mean better overall protection. In fact, full-viscosity oils do not always offer superior protection for modern engines because those engines have tighter clearances and narrower oil passages. For engines that are not more than three years old and meet at least environmental class 4, topping up with low-viscosity oils is usually advised to maintain proper lubrication.

For engines that are structurally older with larger gaps between components, higher viscosity oils may create a more effective wedge in the crankshaft bearings. If the oil film is insufficient in the cylinder-piston area, wear can accelerate and lead to more serious repairs later. Worn engines often require higher-viscosity oils to maintain adequate lubrication—low-viscosity oils can flow away through larger clearance gaps and fail to generate the necessary pressure when the oil heats up.

What oil does my engine need?

Each engine benefits from an optimal HTHS specification. The maxim “more is better” does not apply here. Selecting the right oil requires following the manufacturer’s tolerances, which are listed in the service manual or provided by an authorized dealer. Oil company websites frequently offer online tools to help identify the right grade. Experimental choices, whether very high or very low viscosity, can misfire and cause issues in certain engines.

• Practical guidance and recommendations are often discussed in auto communities and service networks, sometimes even through messaging apps and informal channels.

At the end of the day, choosing the correct oil is about matching the specification to the engine’s design. Proper lubrication supports efficiency, longevity, and reliable performance across varying climates and driving styles. Citations from automotive standards bodies and engine manufacturers provide important context for understanding how viscosity and HTHS influence engine protection and efficiency. (citation: Automotive Standards Institute; engine maker guidelines)