The Skinny on the Current State of Heavy-Duty Engine Oils

As environmental concerns permeate virtually every facet of the petrochemical industry, and the world at large, heavy-duty engine oils are no exception.
BY: Raj Shah and Anson Law
Heavy-duty engine oils lubricate diesel engines, and in the last few years have been subject to numerous regulatory upgrades. Increasingly stringent fuel economy regulations have been presented to formulators, in addition to limits on greenhouse gas emissions. Pollutant exhaust gasses resulting from the combustion of fuel, water and CO2 are omitted by this category. Included are CO, NOx and hydrocarbons, and therefore are subject to legislative oversight. All three pollutants are emitted by gasoline engines; diesel engines also produce particulates that are regulated.
Original Engine Manufacturers (OEMs) in an effort to conform to those restrictions, are employing a combined approach of cooled exhaust gas recirculation (EGR) at higher rates, and exhaust aftercare apparatuses such as catalytic diesel particulate filters and oxidation catalysts.
A new generation of oils has come into existence as a result; they provide emission control system durability, prevent catalyst poisoning and particulate filter blocking, and maintain optimum protection in regard to level of piston deposits, oxidative thickening, oil consumption, high temperature stability, soot handling properties, foaming, and viscosity loss stemming from shearing.
In a collaborative effort, the American Petroleum Institute (API), OEMs, and the American Society for Testing Materials (ASTM) produced an updated diesel engine oil classification for 2007, designated as API CJ-4.
CJ-4 engine oils were explicitly designed for the 2010 model year on highway and Tier 4 non-road exhaust emission standards, and diesel engines of the previous model years. This oil is dedicated for use in all applications regarding diesel fuels with a sulfur content of up to 500 ppm, which is denoted as “low sulfur” grade. While this limit stands, diesel fuels of greater than 15 ppm sulfur content, “ultra-low sulfur” grade, may risk negatively effecting exhaust aftertreatment systems durability and drain intervals.
Aftertreatment systems are a set of components that cleans the diesel exhaust released by the engine before exiting through the tailpipe of the vehicle. These systems are salient in eliminating harmful emissions into the environment and can be feeble in its functions, when the fuel exceeds the sulfur content threshold. Drain intervals are pre-determined timespans for oil changes, to maintain optimal performance and fuel economy. Engine oils requires changing because oils deteriorate over time and can get contaminated. With the goal to uphold an engine’s ideal performance, it is recommended to use fuel with less than 15 ppm sulfur content to avoid plausible hindrances.
More economical and better designed, today’s engines have increased longevity in comparison to the past generations; this results in engines with tighter clearances and closer tolerances, which often get much hotter. Therefore, it is now more crucial than ever that engine oils be immune to the perils of oxidation, shear and aeration. At the vanguard of the latest evolution in engine oil technology, CK-4 and FA-4 oils were designed with the explicit intent to hold up to these trying conditions
“The biggest change in the past few years has been the splitting of the diesel engine oil category into two separate categories,” said Kevin Ferrick, Director of Product Programs, API. “API CK-4 oils succeeded CJ-4 engine oils and are backward compatible diesel oils. Backward compatible means CK-4 may be used where CJ-4 … CI-4, CH-4, and earlier service categories are recommended. API FA-4, on the other hand, is new and intended for engines beginning with the 2017 model year.”
Ferrick states that both oils offer comparable protection, FA-4s possess lower viscosity grades to meet the needs of next generation diesel engines and aid in better fuel economy. In addition, he notes that CK-4 and FA-4 oils both give increased oxidative resistance, shear stability and aeration control in comparison to CJ-4.
CK-4 engine oils are designed to meet the 2017 model year and Tier 4 non-road exhaust emission standards as well as diesel engines of previous model years. CK-4 has the same sulfur specifications as CJ-4 but are superior in maintaining emission control durability at filters and advanced aftertreatment systems. This results from the increased shear stability of CK-4, which aids to protect against viscosity loss.
There are two types of viscosity losses: temporary and permanent. Under high shear conditions, temporary viscosity loss retains to polymers aligning with the flow while permanent viscosity loss retains to the breaking down of the polymer molecules. Viscosity loss has a detrimental effect on the environment because it causes excessive volatilization and oil consumption. Volatilization is the process by which the oil vaporizes, which pollutes the air and weakens emission control.
Oil consumption caused by oxidation is the chemical process where oxygen degrades the quality of the oil and causes it to go rancid. This thickens the oil and makes it less effective in reducing friction and wear in the engine, which promotes corrosion. CK-4 oils are suited to overcome and minimize these issues by being resistant to viscosity loss, which benefits both the environment and the equipment.
CK-4 also reduces oil aeration, which is the process where air is mixed into the oil. Air can be available in three forms: dissolved air, air bubbles, and foam. Dissolved air is the least harmful and is only dangerous if released in the form of bubbles/foam. Bubbles are air pockets submerged in the oil, and foams are air pockets on the surface of the oil. These air pockets are severely detrimental to the engine because it can cause pump captivation, loss of precision control, vibration, filter blocking, and loss of horsepower.
In extreme cases, large air pockets may prevent oils from evenly lubricating all the mechanical components of the engine, which may lead to wear. Oil aeration can be influenced by oil quality in terms of viscosity, density, and age. CK-4 limits these possible detriments by protecting against viscosity loss, and improving the durability/lifetime of the oil. Amongst these salient advantages, CK-4 also protects against catalyst poisoning, filter blocking, engine wear, piston deposits, and degradation of low- and high-temperature properties.
FA-4 engine oils are designed to meet the 2017 model year on highway greenhouse gas (GHG) emission standards. FA-4 are only intended for use in newer on highway diesel engines, and not for previous model years because FA-4 has restricted or no backwards compatibility with engines that uses CJ-4 and CK-4. While CK-4 is essentially an upgraded substitute for CJ-4, FA-4 is used for different engine applications and provides better fuel economy. FA-4 oils emulate all the traits of CK-4, but in addition has a lower viscosity that can perform better under high-temperature, high-shear (HTHS) conditions without sacrificing wear protection.
The maintenance of constant low viscosities reduces resistance of flow and enables the oil to meet stringent fuel efficiency standards. The current oil blend for FA-4 has a HTHS viscosity range of 2.9cP-3.2cP. Older engines require a HTHSV minimum of 3.5cP. Currently, tests are performed to examine the feasibility of using FA-4 oils for engines dialing back to 2010, but results are not yet conclusive. However, FA-4 is highly recommended to use for all future heavy engine vehicles, which will have engines that conform to the low viscosity range. Moreover, FA-4 oil is dedicated for use in all applications regarding diesel fuels with a sulfur content of up to 15 ppm rather than 500 ppm to further conform to environmental regulations.
Although CK-4 and FA-4 oils offer an obvious boon over previous generation oils, it is important for fleets to use the correct oils in each vehicle. While CK-4s are backward compatible, FA-4s should only be used if the manufacturer recommends it precisely for a specified engine. The changeover from previous generation oils to the new standards requires that storage and dispensing equipment be properly labeled.
It is also to be noted that technicians must be adequately notified and trained on this adaptation and all that it entails in order to ensure a successful transition to the heavy-duty engine fuels of the future. MRO
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Dr. Raj Shah is currently Director at Koehler Instrument Company in and the editor of Fuels and Lubricants Handbook and is an elected fellow by his peers at NLGI, STLE, INSTMC, AIC, EI, and RSC. He is also a chartered scientist and a chartered petroleum engineer. Shah is the co-creator of the ASTM hands on fuel technology course and NLGI hands-on grease course, and serves on the advisory board of several universities.
Anson Law is a chemical engineering student at Stony Brook University and a part of the internship program at Koehler instrument company.