Back in 1992, and then again in 2006-2007, diesel fuel lubricity was the buzzword with truck owners. In diesel engines, diesel fuel has always served the essential function of lubricating both injectors and fuel pumps. As the diesel fuel was forced to change with low-sulfur regulations that reduced diesel fuel sulfur from 5000 ppm to 15 ppm over 15 years (that’s a 99.7% reduction if you’re counting), concerns were raised about how the removal of the sulfur would impact the wear and life of these injectors and fuel pumps. The industry responded with a number of excellent lubricity additive chemistries that could be added to the fuel to restore the lost lubricity. Even better, when they started widespread addition to 2-5% biodiesel to the nation’s diesel supply, this went a long way toward fixing the problem, as just a small amount of biodiesel could restore the fuel’s lubricity back to what it was before they took the sulfur out.
This was great for consumers and businesses - now they didn’t have to worry about treating their diesel fuel for lubricity problems. As if they don’t have enough to worry about, right?
Turns out, some of these problems are rearing their heads again.
If you own a Ford or GMC pickup truck from the last ten years, you may know about a class-action lawsuit filed against Ford Motor Company. It alleges that the fuel pumps of Ford Super Duty trucks (especially, ones with the 6.7L Power Stroke) are defective. The suit zeroes in on the Bosch CP4 high-pressure fuel injection pumps and how they allegedly can’t handle the fuel specification for diesel fuel in the United States.
I think this problem surprised some in the petroleum industry who were under the assumption that the biodiesel addition did away with these types of issues.
What Happens To The Fuel Pump?
So this class action lawsuit centers on the Ford fuel pump’s tendency to run on metal-to-metal contact. The theory (alleged by the suit) is that the pump itself forms air pockets during operation. This interferes with the fuel’s lubricating effect, leading to debris and metal shavings coming off and going into the injection systems, leading to expensive problems not limited to total engine failure.
Bosch has made OEM components for many years and their CP4 fuel pumps are well regarded in Europe. They have a reputation for helping with fuel efficiency by pumping less fuel into the engine. But it appears that it only works as well as designed if the fuel has great lubricity - #2 diesel in the United States does not.
The class-action lawsuit alleges that Ford actually could have predicted that these problems would arise. There was a great deal of electronic ink spilled in the 90s and 2000s from all sorts of parties, including Ford itself, predicted possible problems that its customers are now seeing. The suit seeks satisfaction for all those involved.
How much satisfaction? This is not an inexpensive problem. Typical repair bills for this type of failure run from $8,000 to $20,000 per vehicle. Ouch.
How Good Does It Need To Be?
Lubricity in fuel (or any kind of liquid, really) is most commonly measured with an HFRR test. This industry standard ASTM test measures the size of a wear scar generated on a ball bearing after it is subjected to standardized amounts of pressure while in the presence of a lubricant. In the case of a fuel specification, the (diesel) fuel is used as the lubricant. This “lubricity measurement” is part of the ASTM D-975 slate of fuel properties and specifications that legally define what qualities diesel fuel has. In this case, diesel fuel has to have a minimum lubricating quality to it, which is measured objectively by this ASTM Lubricity test. Historically, if the diesel fuel is “ultra-low sulfur”, lubricity was defined as the test’s wear scar having to be under 520 microns in size. The smaller the scar size, the better the lubricity.
Typically #2 diesel without biodiesel or lubricity additives would have a lubricity rating in the low-600s microns. Adding 2-5% biodiesel drops that below the 520-micron standard. Yet, these Bosch fuel injection pumps are having big problems. This must mean that 520 microns isn’t low enough to give adequate protection for these kinds of pumps.
520 isn’t enough? Apparently not enough to protect fuel injection pumps like the Bosch CP4. They and other engine and OEM manufacturers have long maintained that an optimal lubricity rating is well below 520 microns on the HFRR. If you look around for information, 460 microns is the number most often cited as the minimum lubricity rating to protect Bosch CP4 and other kinds of fuel pumps.
What Can You Do About These Lubricity Problems?
Most diesel fuels, even if they have 2-5% biodiesel, won’t reach this number without outside help. There are a number of options on the aftermarket side that can help protect your fuel pump. Rumor has it that Ford even is steering its customer towards its own Motorcraft lubricity additive.
We can’t tell you which one to use, but we would advise that you look for one that specifically references lubricity rating beyond just “helps lubricity”. That’s a generic claim that is easy to slap on a label.
If an additive truly does help lower the HFRR score for diesel fuel, it will contain one of a certain kind of chemistries like a fatty acid, an ester, or an amide. Yeah, we know, most folks wouldn’t know chemistry from a hole in the ground. You’re not expected to decipher technical jargon you’re not familiar with. Just make sure that whatever lubricity chemistry additive you’re considering provides you with more justification on why you should buy it than just “raises lubricity”.
This post was published on November 12, 2021 and was updated on November 12, 2021.