The North American Council for Freight Efficiency has released a new report examining how truck maintenance is evolving during what it calls the “Messy Middle” — the period of transition in which fleets are evaluating cleaner diesel engines, renewable fuels, battery-electric trucks, hydrogen fuel cells and other emerging propulsion technologies.

This is the third installment in HDT’s continuing series examining the report’s findings.

Part 1 looked at how modern diesel engines have become software-driven machines.

Part 2 focused on renewable diesel fuel, which offers fleets a drop-in, low-disruption path to lower-carbon operations.

And in this third installment, we’ll look at why NACFE feels that biodiesel fuel maintenance for fleets is a somewhat different story.

For starters, NACFE analysts note that biodiesel can be a practical, lower-carbon fuel for many fleets. It can use existing diesel infrastructure. And in common blends such as B5 or B20, it can often be used in OEM-approved engines with relatively modest changes to daily operations.

But unlike renewable diesel, biodiesel is not simply petroleum diesel by another name. Its chemistry is different. And because its chemistry is different, its maintenance requirements are different, too.

Biodiesel Is Not Renewable Diesel

NACFE’s report draws an important distinction between renewable diesel and biodiesel.

Renewable diesel is chemically similar to petroleum diesel and meets the same ASTM D975 specification as conventional ultra-low-sulfur diesel. Biodiesel, by contrast, is made up of fatty acid methyl esters, or FAMEs, created through a chemical process known as transesterification.

In that process, vegetable oils, animal fats or recycled cooking oils are reacted with methanol in the presence of a catalyst. The result is biodiesel, with glycerin produced as a byproduct.

That sounds like chemical fine print. But for fleets, it matters.

Biodiesel is governed by ASTM D6751 as a biodiesel blend stock. In commercial fleet use, it is most often blended with petroleum diesel and identified by a “B” number. B10, for example, contains 10% biodiesel and 90% petroleum diesel. B20 contains 20% biodiesel and 80% petroleum diesel.

Higher blends such as B50 or B100 tend to be more limited, often used by captive or niche fleets that can closely manage equipment, fuel storage and maintenance procedures.

That is the first practical maintenance lesson: Biodiesel adoption should be aligned with OEM blend limits, fuel specifications and warranty guidance.

Lubricity Is a Major Benefit

One of biodiesel’s biggest advantages is lubricity.

The process used to produce ultra-low-sulfur diesel removes many of the compounds that naturally helped fuel lubricate pumps, injectors and other precision fuel-system components. Biodiesel can help restore that lubricity.

According to NACFE, adding as little as 2% biodiesel can improve lubricity enough to reduce wear scar measurements below ASTM limits. For technicians and maintenance managers, that can mean better protection for high-pressure fuel pumps, injectors and other expensive components.

That is no small thing on today’s modern diesel engines, where fuel-system tolerances are tight and repair costs are high.

Biodiesel also offers emissions benefits. Because it contains oxygen, it can promote more complete combustion and reduce carbon monoxide, hydrocarbon and particulate matter emissions.

NACFE cites studies showing B20 blends can reduce carbon monoxide and particulate matter emissions by roughly 16% to 17%, while hydrocarbon emissions fall by about 12%.

For fleets under pressure to reduce lifecycle greenhouse-gas emissions without buying new trucks or building new infrastructure, that makes biodiesel an attractive near-term tool.

Storage Discipline Matters

But the same chemistry that gives biodiesel useful environmental and lubricity benefits also creates maintenance concerns.

One of the biggest is storage stability.

Biodiesel oxidizes more quickly than petroleum diesel when exposed to heat, oxygen or light. Over time, that oxidation can lead to gums, sediment and acids that can foul injectors, corrode tanks and plug filters.

That means biodiesel requires disciplined inventory management. Tanks should be kept clean, dry and sealed. Fuel should be rotated regularly. Water accumulation must be monitored and controlled.

This is especially important because biodiesel’s biodegradability, while environmentally beneficial, can also encourage microbial growth when water is present. Microbes thrive at the fuel-water interface, producing sludge and organic acids that can corrode tanks and clog filters.

For fleets, this means biodiesel maintenance is not limited to the truck. It starts in the fuel tank.

Cold Weather Is a Real Concern

Cold-weather performance is another major issue.

High biodiesel blends can gel at relatively mild winter temperatures, depending on the feedstock used to produce the fuel. NACFE notes that high-blend and neat biodiesel can begin to solidify between about minus 3 degrees Celsius and 0 degrees Celsius.

When that happens, wax crystals can restrict fuel flow and clog filters, leading to fuel starvation or engine stalling.

Fleets operating in northern climates must take this threat seriously. Winter blending with ULSD, heated storage, insulated fuel lines and careful attention to cloud point, pour point and cold filter plugging point can all become part of the operating plan.

In other words, biodiesel can work in cold climates. But it cannot be treated casually in cold climates.

Watch Filters During Conversion

One of the most practical technician takeaways in NACFE’s report concerns filter plugging during the first weeks after switching to biodiesel.

Biodiesel has natural solvent properties. When introduced into older storage tanks or fuel systems, it can loosen varnish, sediment and other deposits that have built up over time.

That cleaning action is good in the long run. But in the short run, those loosened deposits have to go somewhere. Often, they end up in the fuel filters.

NACFE says technicians should increase filter-inspection frequency during the first 30 to 60 days after conversion and keep spare filters on hand until the system stabilizes. After that initial cleanup period, filter-change intervals typically return to normal.

That is exactly the kind of detail that can determine whether a biodiesel rollout is viewed as a success -- or blamed for unnecessary downtime.

Oil Dilution Can Change Drain Intervals

Biodiesel also can affect engine oil.

Because biodiesel is less volatile than petroleum diesel, small amounts of unburned fuel can migrate past piston rings and enter the crankcase. That can dilute engine oil, reduce viscosity and accelerate wear if not managed properly.

NACFE notes that fleets using B20 and higher blends may need to shorten oil-change intervals by 20% to 30% and monitor oil condition through routine analysis.

That does not mean biodiesel is harmful to engines. It means maintenance schedules must match the fuel being used.

For maintenance managers, those adjustments should be built into preventive maintenance plans and lifecycle cost models before the fuel is deployed.

A Practical Fuel That Requires Active Management

Clearly, biodiesel as a fleet fuel has a lot going for it.

It can improve lubricity. It can reduce certain emissions. It can use existing diesel infrastructure. It has a higher flash point than petroleum diesel, making it safer to handle and store in many fleet environments. It also supports domestic and regional fuel production, giving fleets another hedge against petroleum supply disruptions.

But NACFE analysts caution that biodiesel is not a “set it and forget it” fuel.

Successful use depends on disciplined fuel quality control, storage management, seasonal blending, filter monitoring, component compatibility checks and oil analysis.

That does not make biodiesel impractical. Quite the opposite. It makes biodiesel a classic Messy Middle technology.

It is available now. It works in existing equipment when used properly. And it can help fleets reduce emissions without waiting for a full zero-emission infrastructure buildout.

But as NACFE’s report makes clear, biodiesel rewards fleets that manage the details properly.