Understanding GM’s dexos1™ PCMO Specification


Most of the leading automakers design newer engine technologies not just to upgrade quality and performance, but also to meet the demands for lower emissions and better fuel economy.

Manufacturers downsize engines and incorporate features such as gasoline direct injection (GDI) and turbocharging to optimize the fuel consumption, these engines are smaller and lighter. They also tend to run hotter and are under more stress than older engines, meaning they need stronger protection. The auto industry looks towards oil producers like Caltex Lubricants to develop new oils that address these evolving demands.

Dexos1 specification:

General Motors, one of the automobile giants, also issues their own sets of requirements for service fill engine oils used in their vehicles. There are two different specification types, dexos1™ for gasoline engines and dexos2™ for diesel engines.

Approved dexos1 oils are mandatory for both, factory fills and service fills starting from 2017 and 2018 GM models. Oils formulated to meet dexos1 specifications are also backwards compatible with older engines. The specification requires that oils meet several of the industry’s most demanding tests, as well as newer tests specific to GM’s requirements.

Dexos1™ oil specification was first introduced in 2010 and then upgraded in 2015. The more stringent dexos1 2015 standard, also referred to as dexos1 Gen 2, sets the requirements for developing oils that can be used with today’s advanced engine technologies.

Dexos1™ Gen 1:

Dexos1 Gen 1 mandated the use of high-quality ingredients, which meant that the conventional ingredients were entirely eliminated. Dexos oils are formulated exclusively with synthetics or synthetic blends, they have better antioxidant technology that keeps oil from oxidizing. These oils generally have a drain interval of up to 15,000 miles and a low viscosity that holds up to engine combustion and heat better and longer than other oils on the market.

Dexos1™ Gen 2:

In addition to the benefits of the Gen 1 oils, dexos1 Gen 2 has improved oxidation and deposit control. The new generation protects engines against what is known as LSPI, which will be discussed shortly. Although most vehicles are approved to use Gen 1, the new Gen 2 oils offer more advanced engine protection capabilities that are not found in the Gen 1 oils. Since the Gen 2 is fully backwards compatible with all the pre-2018 model GM vehicles, all the GM engine oils are transitioning to this formulation.

Specification highlights:

It includes 11 engine tests covering high temperature oxidation, sludge, fuel economy, piston cleanliness, component wear, aeration, low temperature pumpability, etc.

The chemical and physical tests include properties such as viscosity, catalyst compatibility, anti-foam tendency, corrosion, shear stability, etc.

The challenges

Although the manufacturers design engines to be more efficient, a few unforeseen hardware challenges emerged, one of them covered here in detail. Oil producers and our chemical additive suppliers have been collaborating with engine OEMs to address these issues.

LSPI:

LSPI or low speed pre ignition, is the spontaneous ignition of the fuel-air mixture before the spark-triggered ignition. It is an abnormal combustion event in which the fuel-air mixture ignites before intended, causing excessive pressures inside the engine’s cylinders.

LSPI occurs under low-speed, high-torque conditions and can create conditions where the fuel/air ignites too early in the combustion cycle, throwing off the engine’s timing. The expanding combustion charge of the engine collides with the piston as it’s moving up the cylinder, potentially destroying the pistons and/or the connecting rods.

Much of the impetus behind the dexos1 standards upgrade is the LSPI. The higher power density of turbocharged, GDI engines makes them vulnerable to LSPI. In mild cases, LSPI can cause “super knocking” noises, but in the more severe cases it causes engine damage. These result in inefficiencies in the engine and in loss of power and acceleration.

Mitigating the challenge:

Choosing the right motor oil plays a critical role in overcoming these challenges. The dexos1 Gen 2 oil specifications include rigorous GM-specific testing for protection against LSPI, turbo deposits and oxidation, as well as for vehicle fuel economy and aeration. Only the best performing oils in these tests earn the dexos1 approval.

What dexos1 offers:

With the introduction of dexos1, GM has raised the bar and challenged the PCMO industry to step up to deliver new products to address the demand for lower emissions and higher fuel economy. The manufacturers are confident that using a high-quality motor oil with the latest technology, specifically designed to protect GM engines will help maximize their performance.

Moreover, it is good news for consumers and professional installers is that oils that meet dexos1 specifications, such as Chevron’s Havoline ProDS® Full Synthetic, are not strictly “GM oils.” Because they exceed the requirements, they can be used in a variety of applications, including many domestic and imported new model cars. As is the rule, first consult the OEM’s manual for specific oil recommendations. 

David Lee, Ph.D.
About the Author: Dave has over a decade of lubricants experience in Research, Product Development, and technical workshop training. He has a passion for science, and Dave has held various technical positions as a scientist from Greases to Passenger Car and Motorcycle Engine Oils. He loves to talk oils and science, and has been involved in several training workshops giving reason to why people should be excited and care about oils and additives. He’s currently the Consumer Brand Technical and OEM Manager where he’ll be developing the Havoline Engine Oils and Aftermarket Fuel Additives product strategy for the globe. Dave will interface with technology, business colleagues, and customers in support of Consumer Brands. Dave has a Ph. D. in Chemistry, Patents on lubricant composition and manufacture, and extensive engine oil formulation experience.

Other articles you may be interested in.