“Lubricity” is a term that is often used when talking about diesel vehicles. Making sure your diesel fuel has enough lubricity is essential for protecting all the different parts of your vehicle’s engine. But what exactly does it mean, and why is it so crucial to the smooth operation of your diesel? In this guide, we are going to define lubricity, we’ll share some tips on how you can increase it, and we’ll look at the best diesel fuel additive for lubricity.

What is lubricity?

In simple terms, the definition of lubricity is the ability of a fluid to reduce friction between surfaces. The higher the lubricity, the less friction is produced when two surfaces rub together. When it comes to diesel fuel specifically, lubricity is a measure of how well the fuel can lubricate engine components. 

Diesel engines rely on lubrication in order to operate smoothly. Modern vehicles especially are designed with such precision that proper lubrication is vital for smooth operation. Unfortunately, the vast majority of diesel fuel available in the US does not meet the vehicle manufacturer’s requirements for lubricity. This means that the components of your vehicle will generate much more wear and tear than they otherwise would. 

Why does the lubricity of diesel fuel matter?

Every single diesel engine injection system relies on diesel fuel as a lubricant to protect all the moving parts within the fuel system including the injectors, in-line pumps, and injection pumps. If the lubrication of the fuel isn’t good enough, the internal components begin to rub against each other. This leads to increased friction, causing premature wear, potential component failure, and ultimately, costly repairs. Here are the effects that insufficient lubricity can have on your vehicle:

Engine and component wear and tear

Low lubricity in diesel fuel significantly increases the wear and tear on engine components, particularly the fuel injectors and pumps. Because these parts rely on being lubricated by the fuel, without adequate lubricity there will be an increase in metal-to-metal contact. This leads to abrasion and erosion, which is what we call wear and tear. Over time, the cumulative effect of this wear can result in component failure, leading to costly repairs or part replacements.

Reduced fuel system efficiency

Low lubricity in diesel fuel can also decrease the overall efficiency of the fuel system itself. The more friction there is in the fuel injectors, the more energy is required to pump the fuel. This not only results in higher fuel consumption, but it also puts extra unnecessary strain on the engine to maintain performance. This lowers your overall MPG but also leads to the need for more frequent maintenance.

Increased emissions

Poor lubricity in diesel fuel contributes to increased emissions due to the resulting inefficient combustion. Fuel injectors are designed to spray fuel in a fine mist, but increased friction and wear can disrupt this spray pattern, leading to larger droplet sizes. This then causes incomplete combustion, as the fuel is not able to mix thoroughly with the air, releasing higher levels of unburned hydrocarbons and particulate matter into the atmosphere.

Why does modern diesel fuel have less lubricity?

Modern diesel fuel has less lubricity than it used to, and this is primarily due to the process of removing sulfur during the refining process, which also removes the natural lubricating compounds within diesel fuel. This change was brought in to reduce emissions and meet environmental regulations and led to the creation of ultra-low sulfur diesel (ULSD). When sulfur is removed from diesel to create ULSD, the fuel loses much of its natural lubricity. 

Ultra-low sulfur diesel has 97% less sulfur compared to diesel before the change in regulations. ULSD only allows diesel to contain 15 parts per million of sulfur, compared to as much as 5,000 parts per million in traditional diesel fuel. 

The problem with this is that, in order to refine diesel to this level of sulfur, refiners must complete a process called hydrotreating.  This process removes sulfur but also eliminates some of the essential organic components of diesel that provide lubrication to the fuel. After the diesel has been hydrotreated, refineries will treat the fuel with lubricity improvers, but only enough to meet the 520-micron EPA standard.

A key way that the lubricity of diesel fuel is measured in the lab is known as wear scar. It refers to the size of the mark or "scar" left on a metal surface after it has been subjected to friction. A smaller wear scar indicates better lubricity, meaning the fuel provides enough protection against wear by reducing friction between metal parts in the engine.

The Engine Manufacturer’s Association recommends using fuel with a maximum wear scar of 460 microns in order to meet the needs of a vehicle. However, the EPA says that fuel only needs to meet a lubricity standard of a maximum of 520 microns wear scar. This means the fuel you are getting at the pump is only required to meet this standard and is therefore unlikely to meet the lubricity level your vehicle requires.

While reduced sulfur is good for the environment, ULSD fuel doesn’t provide the lubricity levels required to prevent unnecessary wear on your vehicle. This is one reason that many motorists turn to diesel fuel additives. 

How to improve the lubricity of diesel fuel

Like most things, prevention is usually cheaper than the cure. If you want to get the most out of your diesel engine, then preventative maintenance is essential to keeping it on the road as long as possible. Not only does this prevent otherwise avoidable trips to the mechanic, but it will also help to extend the life of your vehicle’s components and save you money in the long run. 

When it comes to lubrication, the easiest and most cost-effective way of keeping lubricity high is to use a specially formulated diesel fuel lubricity additive, such as Archoil’s AR6500 Diesel Treatment. Using it has been proven to reduce the wear and tear of your fuel system, extending component life and preventing the need for costly mechanical repairs. This is even more important for newer vehicles which have much tighter tolerances. 

In independent testing, AR6500 Diesel Treatment increased the lubricity of diesel fuel by 43%, reducing the wear scar by 267 microns. Using the industry standard ASTM D6079 test, AR6500 was tested with fuel that started with a wear scar of 615 microns, and reduced the wear scar to 348 microns, significantly exceeding the engine manufacturer’s recommendation. 

Not only does this diesel treatment lubricate and protect your fuel system, but it also helps to clean your vehicle’s fuel injectors, turbo, and DPF, further reducing the need for maintenance, extending component life, and increasing MPG.

Benefits of using Archoil’s diesel lubricity additive

Reduces friction

Enhancing lubricity plays a crucial role in reducing friction within the engine’s moving parts. By increasing the lubricity of your diesel fuel, there is much less direct metal-to-metal contact, which leads to increased friction and ultimately more wear. This reduction in friction not only ensures smoother engine operation but also improves overall performance and fuel efficiency.

Dissipates heat

Using a diesel fuel additive that improves lubricity also helps to dissipate heat generated within the engine. When friction is reduced, less heat is produced, which helps to maintain optimal engine temperatures. Proper heat dissipation prevents overheating of the engine and the resulting stress on its components, leading to more stable and efficient engine operation.

Maintaining engine cleanliness

These additives also play a vital role in maintaining engine cleanliness. By preventing the formation of deposits and residues on engine parts, they ensure smooth and efficient fuel combustion. Cleaner engines run more efficiently and are less likely to suffer from performance issues.

Improves fuel efficiency

Improved lubricity also directly contributes to better fuel efficiency. When engine components move with less resistance, the engine requires less energy to operate, which in turn reduces fuel consumption. Enhanced fuel efficiency not only saves money but also reduces the environmental impact of diesel engines by lowering the overall fuel usage.

Reduces emissions

Diesel lubricity additives also contribute to lower emissions. Efficiently running engines burn fuel more completely, leading to a reduction in the emission of harmful pollutants such as nitrogen oxides and particulate matter.

Enhanced injector performance

Lubricity additives also enhance injector performance by keeping them clean and lubricated. This ensures that the injectors are spraying correctly, enabling them to deliver fuel more efficiently to the combustion chamber, leading to better engine performance and responsiveness. 

Extended engine life

By protecting engine components from friction, wear, and corrosion, lubricity-enhancing additives significantly extend the overall life of the engine. Engines that operate under optimal conditions with minimal wear are less likely to suffer from serious damage, ensuring they remain functional and reliable for a longer period.

Conclusion

Understanding lubricity and its importance is crucial for anyone looking to maintain and enhance the performance of their diesel engine. By improving the lubricity of diesel fuel with Archoil’s AR6500, you can protect your engine from wear and tear, improve fuel efficiency, and reduce maintenance costs. By choosing the best diesel fuel lubricity additive and using it consistently, you can ensure that your diesel engine runs smoothly and efficiently, providing you with reliable performance for years to come. 

For more great advice from our experts, why not check out our Resources page? We’ve got lots of fantastic guides on everything from diesel fuel to vehicle care and maintenance.