Sylvie Willis
The colour of diesel can vary from clear to red, brown, yellow, orange, blue, or green. While aviation gasoline is deliberately dyed to identify octane rating, diesel fuel only has regional, brand, or batch colour variations. Yellow diesel fuel may indicate a high bio content, which can usually be smelled, or the presence of bacteria or microbes.
| Characteristics | Values |
|---|---|
| Color | Yellow to dark yellow |
| Cause | Oxidation, high bio content, additives, entrained contaminants, age of the fuel, bacteria |
| Odor | Distinctive odor, especially in Oregon |
| Issues | May not pass through filters, may cause engine problems when cold |
| Solutions | Use anti-gel treatments, biocides, or clean containers with soap and water |
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What You'll Learn
Yellow diesel indicates a high bio content
When you notice that your diesel fuel appears yellow, it is often an indication that the fuel has a high bio content. This distinctive colour is a result of the presence of biofuels, specifically fatty acid methyl esters (FAME), which are commonly added to diesel as a renewable and alternative fuel source. The yellow tint is a direct result of the production process of these biofuels, and it is an industry-accepted characteristic of diesel with a high bio content. This colour is not a cause for concern and is, in fact, an expected and regulated feature of diesel fuel with a significant biofuel composition. The addition of biofuels to diesel is a common practice, and the resulting yellow colour is a visible reminder of the presence of these renewable energy sources in your fuel.
The process of creating biofuels, such as fatty acid methyl esters (FAME), involves the use of vegetable oils or animal fats. These sources, when processed, often result in a product with a naturally yellow or light brown colour. This colour is not a dye or an additive but an inherent characteristic of the biofuel itself. The production methods and feedstocks used contribute to this distinct hue. When biofuels are blended into diesel at higher proportions, the yellow colour becomes more apparent and is a direct indicator of the renewable content in your fuel.
The presence of yellow diesel with a high bio content is not just a visual phenomenon but also carries implications for the performance and characteristics of the fuel. Biofuels have slightly different properties compared to traditional diesel, and this can lead to variations in fuel performance and engine operation. The higher the bio content, as indicated by the yellow colour, the more noticeable these differences may become. It is important for users to be aware of these potential variations and choose diesel with bio content that suits their specific needs and equipment requirements.
While the yellow colour is primarily associated with the presence of biofuels, it can also be influenced by other factors. The natural colour of the crude oil from which the diesel is derived can vary, and this can have a slight impact on the final colour of the fuel. Additionally, certain additives or dye markers used for tax or identification purposes can also contribute to colour variations. However, the yellow tint primarily serves as a clear indicator of a higher bio content in your diesel fuel. This colour coding provides a simple visual cue to help users understand the composition of their fuel and make informed decisions about its use and storage.
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Microbes and bacteria can turn diesel yellow
Diesel fuel is susceptible to contamination by microbes, bacteria, and fungi, which can cause it to turn yellow. This contamination is known as "diesel bug" and can occur when water gets into the fuel, creating an environment conducive to microbial growth. Species of bacteria such as Clostridium, Desulfotomaculum, and Pseudomonas, as well as fungi like Aspergillus and Candida keroseneae, can thrive in these conditions.
While it is commonly believed that algae, bacteria, and fungi cannot grow in diesel fuel tanks due to the lack of water, food, and light, this is not always the case. In reality, water can enter diesel fuel through condensation, rainwater penetration, or even absorption from the air, providing the necessary conditions for microbial growth.
The presence of microbes in diesel fuel can lead to several issues. For instance, they can produce biomass or biofilm byproducts that clog filters, requiring more frequent replacement. Additionally, the acidic byproducts of microbial activity can increase corrosion and cause premature wear and tear on engine components, leading to higher oil consumption. Contaminated fuel may also exhibit a noticeable rotten fuel smell due to the production of sulfuric acidic byproducts.
To prevent microbial contamination, it is crucial to control tank water buildup. Products like Bell Performance Dee-Zol and DFS Plus are designed for this purpose. However, even with proper housekeeping, microbial contamination can still occur, especially if there are inconsistencies in fuel handling across the supply chain. In such cases, the use of biocides, such as Bell Performance Bellicide, may be necessary to eradicate the microbes. Regular microbial testing is also recommended as part of a comprehensive fuel care program.
In summary, microbes and bacteria can indeed turn diesel fuel yellow. This discoloration is one of several signs of diesel fuel contamination, along with frequent filter replacements, increased fuel consumption, and a rotten fuel smell. By understanding the causes and consequences of microbial contamination, diesel fuel users can implement preventive measures and maintain the performance and integrity of their engines.
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Regional and brand variations cause different colours
The colour of diesel can vary from clear to yellow to red, and this can be due to several factors, including regional and brand differences.
For example, in the Midwest (IL, IN, MI, WI, OH, and MN), diesel fuel is often yellowish, while in San Antonio, Texas, it is almost colourless. In Arkansas, Tennessee, and Ohio, diesel fuel is very yellow, while in Mississippi, it has been described as bright yellow.
These regional variations may be due to different additives or blends used by suppliers in different states. For instance, biodiesel, which is made from soybeans, tends to be bright yellow, and when mixed with ULSD diesel, can result in a yellowish colour.
Brand variations may also contribute to the colour differences. Some brands may use different additives or blends, resulting in diesel fuel of varying colours.
It is important to note that while colour can indicate the presence of certain additives or blends, it does not always signify a problem with the fuel. However, certain colours like red are used for off-road or agricultural fuel and should be avoided for legal reasons as they are not taxed for use on public roads.
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Bio-diesel is bright yellow
The colour of biodiesel fuel depends on the fatty acid composition of the raw oil from which it is derived. For example, biodiesel obtained from castor oil varies from colourless to light yellow in colour, while biodiesel derived from palm oil can range from light yellow to dark yellow. In some cases, biodiesel fuel can even be dark brown in colour.
To improve the colour of biodiesel, it can be passed through a plant or animal charcoal bed, coconut, or rice bran husk to absorb impurities and enhance the colour. Additionally, washing biodiesel with bleaching agents like clay can make it brighter, although this may compromise the quality. If a colourless product is desired, vacuum distillation is the most effective method.
Yellow diesel fuel can be the result of a high bio content, which is often noticeable by smell. In some cases, the presence of microbes or bacteria, such as iron bacteria that feed on rust, can also cause the fuel to turn yellow. This can occur when diesel is stored for extended periods and microbes start to grow, affecting the colour and consistency of the fuel.
To address the issue of microbes, treatments such as anti-gel or biocides can be used to kill bacteria and fungus in the fuel. However, preventing microbial growth through proper storage and maintenance of diesel fuel is essential to avoid colour changes and potential engine issues.
Therefore, while biodiesel can naturally be bright yellow depending on its source, other factors such as additives, impurities, and microbial growth can also contribute to the colour variation in diesel fuel.
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Anti-gel treatments can be used to prevent discolouration
Diesel fuel can often turn yellow due to oxidation or a high bio content. This discolouration can be prevented by using anti-gel treatments, which also improve the performance of diesel engines.
Anti-gel treatments are a type of additive that can be added to diesel fuel to prevent it from turning into a gel-like substance in cold temperatures. Wax crystals in diesel fuel can drop out of suspension and solidify when temperatures drop, causing the fuel to gel. This prevents the fuel from flowing properly through the engine, leading to performance issues. Anti-gel additives work by lowering the temperature at which the wax in diesel fuel solidifies and preventing the wax crystals from sticking together. This, in turn, improves the flow of the fuel and enhances engine performance.
One popular anti-gel treatment is Hot Shot's Secret Diesel Winter Anti-Gel, which uses three different chemicals: a wax modifier, a wax anti-settling agent, and a military-grade de-icer. The wax modifier reduces the point at which wax in diesel fuel solidifies, while the wax anti-settling agent keeps the wax dispersed. The de-icer component disperses moisture, preventing it from clogging and freezing fuel filters. This treatment is safe for use in all diesel engines, including those in semi-trucks, marine vehicles, and agricultural equipment.
Another trusted option is Howes Diesel Treat, which is an anti-gel and fuel conditioner. It effectively removes water and prevents gelling, even in extremely cold climates. This product is also alcohol and solvent-free, providing protection without the use of harmful chemicals. Diesel Treat improves lubricity, prevents deposits, and enhances the performance of diesel engines.
By utilising anti-gel treatments, diesel fuel discolouration can be prevented, and engine performance can be optimised, particularly in cold weather conditions. These treatments are essential for maintaining the functionality and longevity of diesel engines.
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Frequently asked questions
Yellow diesel fuel is usually indicative of a high bio content, which can often be smelt. This is especially common in Oregon, Arkansas, Tennessee, and Ohio.
Yes, it is normal for diesel to be yellow. While the preferred colour is clear, diesel can come in a range of colours, including red, brown, orange, blue, and green.
While the colour of your diesel may not directly impact your engine, it is important to ensure that you are not using off-road fuel in your vehicle, as this can result in large fines. It is also important to regularly clean your fuel containers to prevent the buildup of microbes.
To prevent your diesel from turning yellow, you can treat it with an anti-gel product. Additionally, ensuring that your fuel is stored in optimal conditions and that your containers are clean can help to prevent the growth of microbes and oxidation, which can cause discolouration.
