A Closer Look at Biodiesel

Biodiesel offers a few benefits, like increased lubricity and cetane, but it also presents challenges. Here's what you can do.

April 9, 2020

Presenting a renewable option for diesel engines, biodiesel is formulated from vegetable oils and animal fats, with blends up to B20 approved for use by many major engine manufacturers. Biodiesel presents environmental benefits and some performance improvements over conventional ultra-low-sulfur diesel (ULSD) fuel. Like many benefits, however, they come with some tradeoffs.

Biodiesel Benefits: Increased lubricity

Lubricity is critical for controlling wear in fuel pumps and injectors.

While diesel fuel has traditionally had high lubrication properties, the desulfurization process used to strip the diesel fuel of the sulfur content to meet ULSD requirements also strips the fuel of some of the organic compounds responsible for lubrication.

Biodiesel does not go through this process and has different compounds responsible for lubrication.

Higher cetane

Diesel engines operate best on fuel with cetane values of 50 or higher, allowing for a more complete burn and preventing ignition delays.

Most diesel fuel sold in North America, however, has a cetane value between 40-45. Biodiesel offers higher cetane values.

Biodiesel derived from vegetable oil typically has a cetane value between 46-52, while biodiesel derived from animal fat typically has a cetane value between 56-60.

Biodiesel Challenges

While offering benefits, biodiesel also presents a number of challenges:

Decreased fuel efficiency

Because it has lower energy density, use of biodiesel can reduce fuel efficiency and power output.


Injector deposits

Biodiesel heavily increases the potential for injector deposits.

Specifically, the sodium used as a catalyst in the manufacturing process contributes to the formation of metal carboxylate deposits inside the injector, which can reduce engine power and performance and contribute to injector failure.

Fuel stability

Biodiesel is less stable than conventional diesel fuel, which can contribute to undesirable odors, increased acidity and increased viscosity.

Degradation products can lead to increased corrosion of fuel-system components and polymer, gum and sediment formation that causes fuel-filter plugging, injector deposits, lacquering, increased smoke emissions, decreased fuel economy and decreased horsepower.


Biodiesel attracts water, which breaks down the fuel, makes it more acidic and supports microbial growth.

Microbes contribute to fuel-system plugging (especially the filter) and increased corrosion.

Cold-flow performance

Biodiesel gels at higher temperatures than traditional diesel fuel, eventually clogging the fuel filter and starving the engine of fuel, preventing it from starting.

Diesel Gas Pump

Problem resolution

Problems created by ULSD and/or biodiesel fuel can be addressed in two ways:

1. Component replacement

Failing to address issues associated with using ULSD or biodiesel can result in expensive and inconvenient performance issues and repairs.

• Reduced performance (horsepower, fuel economy, starting, reliability)
• Inconvenience of being stranded on the side of the road
• Expensive towing bill
• Expensive repair bill
• Equipment downtime

2. Fuel additive preventive maintenance

A variety of diesel fuel additives are available to help diesel owners mitigate diesel fuel issues.

The chart below breaks down the fuel additives available on the market, their benefits and the corresponding AMSOIL diesel fuel additives that provide the specific benefits.

Biodiesel and diesel fuel additives.

The AMSOIL solution

Biodiesel has upside but carries significant challenges as well.

Fortunately, AMSOIL diesel additives provide a convenient, cost-effective way to mitigate these issues.

Diesel Injector Clean

  • Targets traditional nozzle deposits, combustion-chamber deposits and internal-diesel-injector deposits found in HPCR injectors
  • Lubricates to reduce fuel pump and injector wear
  • Concentrated for rapid results, maximum horsepower and up to 8 percent increased fuel economy in engines with accumulated deposits
AMSOIL Diesel Injector Clean

Diesel Cetane Boost

  • Raises the cetane number of diesel fuel up to eight points for maximum horsepower, increased fuel economy and easier starts in all diesel engines
Diesel Cetane Boost

Diesel Cold Flow

  • Effectively modifies wax crystal formation at low temperatures to depress diesel fuel pour point, prevent wax settling and improve cold-flow filtration properties
AMSOIL Diesel Cold Flow

Diesel All-In-One

AMSOIL Diesel All-in-One

Diesel Injector Clean + Cetane Boost

AMSOIL Injector Clean + Cetane Boost

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