API’s heavy-duty categories provide a particularly interesting case study on the development of new, lower-viscosity lubricant technologies and the end-use market’s willingness to accept and buy cutting-edge formulations. Among both OEMs and end users, there has been hesitation to fully embrace FA-4 certified lubricants as a solution to achieving greater fuel economy, despite the rigor that has gone into their development. This has been disappointing, especially considering the potential benefits. It has been shown that Class 8 over-the-road fleets can realistically expect fuel savings in the range of 0.5%-1.5% by simply switching from an API CK-4 15W-40 formulation to a 5W- or 10W-30 engine oil. (15W-40 lubricants represent the majority of market share.) In addition, the savings from switching to the fuel-efficient API FA-4 variant can be expected to add an additional 0.4%-0.7% of increased fuel efficiency.

Experimental Development and Lab Testing 

The product life cycle begins with experimental ideas to meet needs found in the marketplace. Recently, changes to fuel, lubrication and filtration were necessary for compatibility with advanced hardware, including fuel injectors and advanced exhaust aftertreatment promising lower emissions and fuel consumption. Formulators consider these needs during the initial development process and begin an experimental testing phase to determine reliable ways to certify performance levels required by the new category. This process involves considerable time and resources to establish the parameters of the new category, helping to satisfy the needs of evolving engine hardware.

Early concept evaluation takes place virtually using various computational tools. Lubrizol deploys its proprietary modeling software to make initial determinations. This modeling software allows our teams to identify ideal ways to meet and exceed technical needs and specifications. Initial formulations that demonstrate merit based on predictions of functional performance—as well as target costs for development—proceed to standard lab bench testing. 

Pending successful results at this level, testing in actual hardware is scheduled. These tests are typically isolated to test bays. Testing is further carried out on real engines and a full dynamometer by various stakeholders. For example, through the development of CK-4 and FA-4, Lubrizol performed extensive dynamometer testing at its Wickliffe, Ohio, headquarters. Prototype formulations demonstrating acceptable results proceed to the field-testing phase. 

The Value of Field Trials

Before describing field trials themselves, it’s important to note that formulations making it to this stage have already thoroughly demonstrated the desired performance characteristics in lab tests. Field testing proceeds with the assumption that the formula has already been optimized and seeks to validate performance adequacy within the intended application. Here, real-world results are generated, evaluating the performance of lubricants and additives to meet or exceed all performance measures in true, real-world conditions.

Field testing is also fundamentally different from lab testing. In the lab, statistical rigor results from running an experiment repeatedly while holding environmental conditions constant; the only variable is the additive technology. In field testing, it is hoped that the trials will result in real-world confirmation of the qualities expected. Some of these qualities include protection under extremes of load and speed; control of losses due to heat buildup or contaminants; extended useful life; and special protection systems protecting older equipment. Elsewhere, field tests can help uncover unintentional circumstances users may encounter. Coolant may be found in the oil sample. A sample may not have been extracted on time. The wrong amount or type of oil may have been added at the last time of service. High silicon may be found in the sample, meaning that it’s time for the truck to swap its engine air filter.

A field trial can involve a limited number of simultaneous experiments. For example, a large off-highway asset, like an aggregate hauler, may have over a half-dozen lubricant-carrying compartments. A basic suite of oil analysis measures, regularly obtained, may provide all the confirmation of performance sought. On the other end of the spectrum, the investigation could warrant capture of huge amounts of data. Valuable information can be obtained through capture of data from the engine control module in modern engines. Telematics systems fitted on most vehicles can provide some details on routes and elevation. 

Executing a Successful Field Trial

A sound field trial begins with a thoroughly scoped plan. The scope includes a description of trial objectives, site information, definition of formulations and assets to be tested, trial timing and duration, measurements to be made and expectations of each actor. 

Strong partnerships are essential. Lubrizol is fortunate to maintain long-standing relationships with several commercial fleets. Fleets must be proactive; our teams require they change their oils at regular intervals and take samples to submit to our teams for analysis. Our technicians are in regular conversation with each fleet throughout the trial. Inspections of one or more of the units may be contracted to occur. In a heavy-duty diesel engine, this would typically involve an in-frame refresh of the engine, allowing for the cylinder liners, pistons, bearings, oil pump and certain other parts to be removed for inspection. All observed results from the trial are then summarized in a detailed report. 

Of course, fleet budgets often dictate a limit on quantity of units participating in a trial—these partners have a business to run, after all. Vehicles may also be lost to attrition or early trade-out. A good rule of thumb for a successful field trial is to maintain at least two trucks running the prototype product and at least one running as reference. Field trials aimed at a specific focus of performance may run only a brief period of time—under two years. There may be very few duplicate units running and there may or may not be a reference running in any of the units. 

Trials are often over a lifetime. This can be the lifetime under warranty, which for linehaul vehicles is often 500,000 miles, or the complete life the fleet owns the equipment. The most elaborate field trials coincide with scheduled introductions of lubricant industry standards—like API CK-4 and API FA-4, and with the next API category. In this case, many vehicles of many different types, along with various formulations and grades, are simultaneously monitored.

At Lubrizol, we perform this kind of analysis with lubricants that have run in trucks all around the United States because we know that some miles are more severe than others. Heavy-duty service is not as strenuous in the Midwest as it is in the Rocky Mountain region, for example. Throughout all this work, our teams are primarily seeking to identify any premature engine wear that may have resulted from the lubricant performance. We look at the oil itself to identify any potential premature oxidation, unwanted viscosity increases, or excessive amounts of wear metals within the drain oil. 

Field Testing for Fuel Economy

Due to the potential real-world variables described, fuel economy gains achieved via the lubricant can be one of the most elusive performance characteristics to accurately measure. This is particularly important in the case of API FA-4, or any engine oil performance category that seeks to deliver fuel efficiency as a performance benefit. 

To those ends, during the development of API FA-4, Lubrizol conducted real-world fuel economy trials that sought to demonstrate a balance between experimental rigor and real-world variation. With some in the vehicle industry questioning the legitimacy of in-lab fuel economy tests, we set out to make such measures in real usage. Test vehicles were fitted with highly resolute torque and fuel consumption sensors. Acceleration schedules, bucketed from histories of real-world usage of similar vehicles, were programmed in, eliminating human variability of repeated identical accelerations. The vehicle was operated on a long, level test track. An operating window of weather, including wind speed, was established. Maintenance was closely monitored and many other measures, like exhaust differential pressure, were captured. Oil was changed out between reference and candidate, the process repeated several times, and the data normalized and analyzed to reveal differences in efficiency.

This is an example of a field trial with variation removed wherever possible and did lend itself to some degree of statistical investigation. During a multi-year, on-highway field trial, fleet vehicles filled with FA-4 10W-30 oil experienced 1.9% better average fuel economy than those that used CK-4 15W-40. These fleet vehicles were driven hundreds of thousands of miles over the trial to take into consideration various driving conditions and seasons.

The Future for Lower-Viscosity Formulations 

Over the course of the current API category’s initial development to today, Lubrizol has field tested FA-4 lubricants in more than 400 individual engines over the past decade, generating more than 75 million miles of data. Trucks tested include new models designed to be filled with FA-4 lubricants and older-model trucks where FA-4 is not specified by the manufacturer. Through this testing, we have seen heavy-duty fleets achieve significant fuel economy savings while providing their trucks with outstanding protection. 

The bottom line is that FA-4 lubricants—and such technologies that will succeed them—offer tremendous benefit to lubricant customers. Extensive testing proves it, and it will require our ongoing development and compelling advocacy to see their wider application and acceptance.   

John Loop is the OEM liaison for Lubrizol. 

Kris Meekins is a testing engineer for Lubrizol.