Motor engines depend on lubricants and oils — together with quality fuels — as their primary source of vitality, particularly when it comes to longevity and sustained performance. The impact of lubricants on engine behavior is substantial, directly determining whether an engine operates at its full potential or suffers due to inadequate lubrication. These substances also play a decisive role in the durability of your equipment. Engines paired with the correct oils tend to last longer and demonstrate superior performance capabilities.
Among the most critical considerations when selecting an engine lubricant is the viscosity of the oil.
Consistently using engine lubricants with the correct oil viscosity — meaning an appropriate viscosity index suited to your specific engine — reduces vehicle downtime and helps keep maintenance expenditures under control.
Oil viscosity refers to the degree to which a lubricant resists flow and shear. This characteristic is shaped by a number of factors including:
Two primary categories of oil viscosity exist: dynamic viscosity and kinematic viscosity (also referred to as absolute). Dynamic oil viscosity describes the property that determines how much force is required to initiate lubricant flow. Kinematic viscosity, on the other hand, reflects how rapidly the lubricant flows once internal engine forces are applied.
The units used to measure dynamic and kinematic oils:
The oil Viscosity Index (VI) is a measure of how significantly temperature affects viscosity levels.
A fundamental principle applies here: as temperature rises, viscosity decreases, and the reverse holds true as well. This means that both the formulation and the quality of engine oils are essential factors when selecting the appropriate product, as these attributes govern how the viscosity of motor oils diminishes in response to increasing temperatures.
The Viscosity Index communicates the rate at which a temperature shift causes viscosity to change. Understanding the VI of a given oil is therefore essential, as it reveals whether the lubricant is capable of meeting your engine's demands across its expected operating temperature range.
Calculating the viscosity index of engine oils involves measuring kinematic viscosity at both 40°C and 100°C, then comparing those values against two established reference oils.
As a reference point, conventional mineral oils typically fall within a viscosity index range of 95 to 100, whereas highly refined (hydrotreated) mineral oils can reach VI values of up to 120. Hydrocracked and synthetic lubricants often surpass 120, with fully synthetic formulations reaching as high as 140. At the lower end of the spectrum, naphthenic oils carry the lowest viscosity index at 80.
As noted earlier, oil viscosity shifts in direct response to temperature changes. Lubricants with a low VI undergo a sharp decline in viscosity when exposed to heat, while high VI oils exhibit only minimal viscosity reduction as temperatures climb. This characteristic makes high VI oils considerably more stable and therefore far more preferred.
As discussed in the previous section, engine oils with a lower viscosity index may provide adequate lubrication within certain temperature ranges, but they become insufficient under higher-temperature conditions because their viscosity drops sharply as heat builds up.
When an engine operates with oil that lacks optimal viscosity, mechanical friction and component wear rise considerably due to the breakdown of the lubricant film. Prolonged use of low VI lubricants in engines that require high viscosity oils can diminish performance output, increase downtime frequency, and ultimately shorten the operational lifespan of the engine.
Before purchasing any oil or lubricant, it is strongly advisable to consult the manufacturer's oil specifications for your engine, equipment, or machinery, and then select an oil whose viscosity index aligns with those requirements.
Be sure to factor in both the operating environment and prevailing climate conditions as well. It is also worth considering the oil weight when narrowing down the right choice for your engine.
Ultimately, selecting a lubricant with the correct VI is fundamental to protecting both the performance and the longevity of your engine.
Valvoline's core mission is to supply machinery and vehicle owners with nothing less than the finest products available.
Some of our high viscosity oil products include:
Our lineup extends well beyond the products listed above and encompasses only top-tier high viscosity engine oils along with other comparable products designed to help your equipment reach peak performance and enjoy an extended service life. Backed by over 150 years of industry experience, customers trust that every Valvoline product undergoes meticulous development and rigorous testing.
Our premium-quality oils are the result of genuine dedication, deep-rooted expertise, and continuous innovation. Valvoline employs only advanced technology, and every lubricant-based product we offer is carefully selected and field-validated by our teams of expert researchers. All testing takes place within our state-of-the-art facilities, ensuring that our products consistently deliver maximum performance, minimal downtime, and cost efficiency.
At Valvoline, your priorities matter to us, and we are committed to the same objectives you hold — keeping your machinery and equipment running reliably through the most demanding conditions and the harshest environments.