What You Need to Know About GM’s Motor Oil Spec
General Motors’ dexos brand of engine oil has been out since 2011. The question many have is why GM developed their own oil specification. After all, they are members of the International Lubricant Specification Advisory Committee (ILSAC) group of automotive OEMs. They have sponsored API GF series engine oils, which includes the current API GF-5, as well as the more familiar API service categories, the most recent of which is API SN and SN-RC.
This all started back in 2009 when GM started to analyze their resource issues with the idea to reduce engineering, testing and validation. This study was global and addressed timing and financial concerns. At the time, GM had a number of internal engine oil specifications that created logistical problems. What was originally called “GEOS” was expected to create engine oil specifications that were global; which would eliminate replication of the resources that were being used to develop and maintain multiple specifications. By creating a single oil specification, GM would be able to ensure oil quality for engine development and production globally.
GM believed that by testing and validating engines with GEOS on a global basis, they would improve quality and create greater customer satisfaction. In addition, the new oil would allow for faster development of engines with improved fuel economy and emissions, as well as optimized drain intervals. GM didn’t give up on ILSAC specifications, but the global reach of GEOS was a large inducement to move forward.
According to GM, engineers from around the world identified engine oil characteristics that they thought were important for their engines. They selected the oil improvements that were needed to address their current and, more importantly, future needs. Then, they selected tests and limits that would address the needs that had been identified.
By the time the first tests and specification had been developed, the brand name had become dexos. dexos1 is GM’s global engine oil specification for gasoline engines, which replaced GM 4718M and GM 6049M. Although it was specified for all GM vehicles starting with the 2011 model year, it was also promoted as an excellent choice for previous model year vehicles.
According to GM, oils meeting the dexos1 specification exhibit enhanced performance compared to many oils on the market today. In fact, the dexos1 specification is made up of a combination of some of the most demanding tests found in industry specifications, such as those from the American Petroleum Institute (API) and the European Automobile Manufacturers Association (ACEA).
One of the advancements in engine oil for dexos1 was the introduction of a viscosity grade (SAE 0W-20) that was not recommended at the time. GM apparently thought they would be recommending this grade in the near future and included it in dexos1. It was being recommended by Japanese automakers. SAE 5W-30 was the recommended oil viscosity at the time.
By 2015, GM was ready to introduce dexos1 Gen2. This product was an improvement over dexos1 and included tests that will be a part of the long-awaited GF-6, which is currently targeting for introduction in 2020. Two major improvements from the original to Gen2 were the introduction of another non-specified viscosity grade, SAE 0W-16, and the introduction of a low speed pre-ignition test. In addition, GM also added an engine test measuring resistance to aeration. This latter test was added because new GM engine designs utilizing variable valve timing require the engine oil to also act as a hydraulic fluid. Air entrainment in this type of application can seriously degrade the operation of the valve system.
The issue for OEMs in general, and GM in particular, is they believe the current process (ILSAC/API) is too slow to react to changes in the marketplace. As everyone knows, fuel economy and emissions reductions are the driving forces for significant change in vehicle and engine design, not to mention transmissions. Both of these parameters are interconnected and are due for major tightening of limits between now and 2025.
Fifty years ago, engines delivered about 0.5 HP per cubic inch of displacement. That’s why high-displacement engines ruled. A 283 CID engine would deliver about 140 HP. Today, engines are delivering 1.5 or more HP per cubic inch! That means a 93 CID (1.5L) engine would be able to deliver the same 140 HP. In addition, these smaller engines have very sophisticated fuel delivery systems such as stop/start, variable valve timing and gasoline fueled, direct injection, with turbochargers. On top of that, low speed pre-ignition is an existing problem with the newer engines. All of these systems require substantially better engine oils.
GM dexos1 Gen2 is a combination of API tests and ACEA (European) tests, with some GM-specific tests included. Simply stated, that means it is ILSAC/API GF-5 and API SN Plus. In some cases, the test limits for dexos1 Gen2 are more stringent than the API limits. GM continues to evaluate new engine designs and seeks to improve their oil recommendations to protect the latest engine configurations.
Getting down to oil formulation specifics: there are some fundamental issues regarding engine oils that should be addressed. In order to successfully blend an SAE 0W-16 with 13 percent maximum volatility, there are some specialized base oils needed. The simple fact about base oils is that with lower viscosity, there is an increase in volatility. In order to meet lower volatility limits, either synthetics or carefully manufactured base oils are required. The cost differential between true synthetics and conventionally refined base oils is significant. The solution to that is to make a finished oil that is a blend of the two, based on viscosity versus volatility. It’s not easy, but it can be done.
Once the base oil combination is selected, the additive chemistry needs to be developed. For dexos1 Gen2, special attention is needed to meet LSPI and variable valve timing issues. Additional oxidation resistance, as well as limited metallic ash content, have been shown to impact both of these tests. Of course, the need for dispersants, enhanced foam inhibitors, antiwear additives, friction modifiers, pour point depressants and viscosity modifiers still remains. All of this needs to be carefully balanced — which is a major undertaking. That’s why additive companies spend so much time and resources to develop new additives for any new or additional specification requirement.
Some have asked if a booster additive can be added with current oils to meet dexos1 Gen2. That would be a great solution to the logistical problem. Unfortunately, it can’t be done. Each additive system has a unique combination of components that are really balanced on a technical knife’s edge. If an additional material or booster is added to the system, it is likely to upset everything — and what was once an approved API category product is now untested and not approved.
So the bottom line to the dexos1 Gen2 story is that it is a carefully created product for GM’s engine oil needs and reflects their desire to have a single engine oil to recommend globally. It also helps satisfy their need to move quickly when new hardware is developed for their marketplace.
While dexos1 Gen2 is the most widely recognized of the specific OEM oils, it is not the only one. The Japanese engine oil market is based on what is called “Genuine” oils. These are engine oils designed and tested by the OEM and recommended strongly for their engines. Toyota, Honda, Nissan and others all use this system. The oils are not necessarily the same in performance as the API/ILSAC oils. Each engine manufacturer has their own special interests and formulates their oil for specific performance needs or wishes. The European automakers also specify engine oils according to their own specifications, just as GM does. The ACEA engine test protocols define market-general oils, while individual OEMs require additional testing.
There is a trend occurring in the North American oil marketplace, which looks more and more like the GM system. It may not be too long in the future before we return to the 1950s and 60s when every OEM had their own oil. Oil marketing is sure to be a challenge.