Smart Pouring: Why it is Important to Stick to the OEM Recommended Viscosity

We’ve all been taught that the single most important property of any lubricant is viscosity. Why is that? Since the four primary purposes of an engine oil are: 1. Lubricate, 2. Clean, 3. Cool and 4. Protect, it stands to reason that the proper viscosity will maximize lubricant performance in all four aspects. But what happens when the proper viscosity isn’t used?

If the viscosity is too low, the critical surfaces in an engine will be subjected to increased metal-to-metal contact. That would mean increased friction and wear. It also might cause engines to run hotter. On an operational basis, the performance in such areas as fuel economy will suffer if the viscosity is too low and an insufficient oil film will not form. The ability of the oil to keep the engine clean could be hampered, because the likely higher operating temperatures will degrade the additive package sooner.

If the viscosity is too high, the engine may have more surface protection but performance will be degraded due to increased (viscous) friction. Again, cooling may be impaired, and higher operating temperatures could shorten oil life.

While they don’t directly measure viscosity, oil life monitoring systems used by the OEMs would react to the increased temperature of operation. It’s possible for the wrong oil viscosity to cause the OLM to call for an oil change sooner than normal.

Here’s another factor to consider. The OEMs design and prove out their new engines using a specific viscosity grade. Most recently, the new turbocharged gasoline fueled direct injection (TGDI) engines were initially designed to operate on SAE 5W-30. As new engines are developed and introduced, it is possible that SAE 0W-16 could become a preferred grade, but not at present.

The Coordinating Research Council (CRC) recently published a report on wear in stop-start engines, which are designed to turn off when the vehicle is at a complete stop such as a stop light. When the accelerator is pushed, the engine restarts. This design saves a fair amount of fuel, especially in urban use. CRC’s test results showed higher wear with lower viscosity oil (SAE 0W-16) than the recommended SAE 5W-30. The OEMs weren’t surprised at the result and say that the CRC’s test results show how important it is to use the recommended engine oil viscosity.

The OEMs go on to say that engine design is tightly tied to viscosity grade. That means building engines in which SAE 0W-16 and thinner oils are recommended must be with components that are designed to maintain proper oil flow with such low viscosity oils.

The OEMs make recommendations as to which viscosity grade is preferred, and they reserve the right to deny warranty claims if the wrong viscosity (or category) oil is used. Generally, there isn’t a big push to deny claims, but for the newer engine designs, it may become a greater possibility. Using the proper viscosity and category when changing oil is the smart bet for installers.

Currently, API has licensed a total of 35 different brands of SAE 0W-16 API SN engine oils. Of these, 10 are US brands. Asia Pacific has 20 branded oils. By contrast, there are 364 licenses for SAE 0W-20 SN products, of which about 80 percent are divided equally between North America and Asia Pacific.

In general, all of the automakers call for SAE 5W-30 or SAE 0W-20 engine oil. Toyota is one of the few automobile manufacturers recommending SAE 0W-16, but only for their L4 engines, such as those found in the 2018 Camrys. They will allow SAE 0W-20 as makeup oil but only until the next oil change. Honda also calls for SAE 0W-16 or SAE 0W-20 for their Fit engine. For all other engines, both Honda and Toyota recommend SAE 0W-20. For certain TDGI engines, SAE 5W-30 is the preferred viscosity grade.

It’s important that not only the proper viscosity grade be used, but the OEM recommendations for performance must be met as well — such as API SN Plus. GM specifies dexos but accepts API SN Plus (GF-5). Many foreign OEMs have their own oil requirements but generally accept API SN Plus (GF-5). The SAE 0W-16 viscosity grade will be API SN Plus but will not have an API starburst until GF-6, which is expected to be introduced sometime in 2020.

For those few four-cylinder Toyotas and other vehicles that call for SAE 0W-16, it would probably be a good idea to carry a few cases of an available SAE 0W-16. The following list identifies the companies with current API licensed products (as of press time) that have API SN Plus, SAE 0W-16 available here in the United States.