Katerina Swanson
It's important to be able to identify bad diesel fuel to maintain the performance and longevity of your engine. While diesel fuel can be stored for 12 months, improper storage, such as exposure to warmer temperatures, can lead to fuel degradation. Water contamination is a common issue, caused by rainwater getting into the diesel tank through an open fill point or vent, or condensation. Water in the fuel system is problematic as it sinks to the bottom of the tank, creating an environment for the growth of bacteria known as diesel bug, which produces nasty sludge that can block filters and damage the pumping system. Microbial growth can also lead to the formation of diesel algae, a slimy substance that can clog your fuel system. Other signs of bad diesel fuel include discoloured fuel, a foul odour, excessive smoke, and engine performance issues such as rough idling and lower fuel efficiency.
| Characteristics | Values |
|---|---|
| Unusual Odor | Good-quality diesel fuel should have a mild, nearly odorless scent. If you detect a strong, pungent smell resembling rotten eggs, it is a clear indication of contaminated or degraded fuel. |
| Decreased Fuel Efficiency | A sudden drop in your vehicle’s fuel efficiency can be an early warning sign of bad diesel. |
| Engine Performance Issues | Poor-quality diesel fuel can lead to various engine problems, including rough idling, frequent stalling, or reduced power output. |
| Fuel Filter Problems | Contaminated fuel can clog the fuel filter, resulting in reduced fuel flow and decreased engine performance. |
| Fuel Appearance | Discoloured fuel is a bad sign. If it's darker than usual, it could indicate the presence of contaminants. |
| Water in the Tank | Water in the tank is a common issue caused by rainwater, condensation, or leaks. It can cause major problems, as water doesn't burn or compress. |
| Fuel Contamination | Water in the tank can lead to the growth of microbes, fungus, bacteria, and "diesel algae," which can contaminate the fuel. |
| Fuel Dilution | Diesel fuel mixed with gasoline or another solvent can damage the engine. |
| Improper Storage | Improper storage, especially in warm locations, can lead to fuel degradation. |
| Sludge Formation | Water contamination can lead to the formation of sludge, which can block filters and damage the pumping system. |
| Exhaust Smoke | More than the usual amount of exhaust smoke, especially white smoke, can indicate bad diesel fuel. |
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What You'll Learn
Water in the fuel tank
One of the easiest ways to check for water in your diesel fuel is to open your tank and look inside. Diesel that is contaminated with water will often appear noticeably darker than usual. You can also look for fuel cloudiness, which indicates the presence of emulsified water dispersed throughout the fuel. If you suspect there may be water in your fuel, you can also purchase a water-dispersing formulation to treat the diesel fuel and prevent engine issues.
Water in your diesel fuel can cause rough starting and erratic idling, as well as black or white exhaust smoke. It can also lead to more serious issues, such as frozen fuel pumps and lines in cold weather, or even complete engine failure. Water provides an environment for bacteria and microbes to grow and multiply, which can corrode the fuel tank and clog fuel filters.
To prevent water from entering your fuel tank, it is important to regularly inspect your tank, filler cap, and fuel filler lines for any leaks. You should also have your diesel serviced regularly and ask your mechanic to inspect and empty the water separator, which is designed to collect large amounts of water.
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Unusual odour
Good-quality diesel fuel should have a mild, nearly odourless scent. Unusual odours can be a clear indication of contaminated or degraded fuel. If you detect a strong, pungent smell resembling rotten eggs, it is likely that your diesel fuel has been contaminated or degraded.
Diesel fuel can be contaminated by water, which can enter fuel storage tanks through condensation, leaks, or missing fuel caps. Water can settle at the bottom of the tank, degrading the fuel and potentially damaging the engine. Water can also harbour microbes, leading to the growth of bacterial and fungal contaminants known as "diesel algae" or "diesel bug". These microbes can clog fuel filters and cause engine malfunctions. The metabolic waste products from these microbes can result in a sour or rancid smell.
Fuel dilution is another potential issue, where diesel fuel is mixed with gasoline or other solvents. This contamination can alter the fuel's composition and lead to engine problems. Discoloured fuel, with a darker or reddish hue, is often a symptom of degradation and the presence of impurities.
Improper storage conditions, such as exposure to extreme temperatures, sunlight, and air, can also accelerate fuel breakdown and compromise its quality.
In severe cases, contaminated diesel can cause complete engine shutdown, clogged fuel injectors, and internal component wear and tear. Regular engine inspections and maintenance are crucial to mitigating the impact of bad diesel.
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Discoloured fuel
One of the most visible signs of diesel fuel degradation is a change in colour. Fresh, undyed diesel fuel is typically an amber-green colour. If the fuel appears darker, this indicates that the fuel has started to degrade significantly. This is because the heavier components of the fuel blend are no longer dissolved in the fuel but are coming out of the solution and floating freely in the fuel, giving it a darker colour.
Discoloured diesel fuel is often referred to as "dirty diesel fuel". This term describes diesel fuel that has been contaminated or degraded, often due to oxidation reactions, microbial contamination, or the presence of water. Dirty diesel fuel can cause problems in your engine and fuel system, leading to injector deposits, clogged filters, and reduced fuel efficiency.
To prevent diesel fuel degradation, it is important to treat the fuel with stabilizers and remove any water from the tank. Using biocides to kill any microbial contamination is also essential. However, if your diesel fuel has already discoloured, there are a few things you can do to try and fix the problem. One option is to use a fuel filter to strain the fuel and remove any large contaminants. Additionally, you can try using a multifunction diesel additive with detergency to help resolve the issue.
It's important to note that diesel fuel can last for years if it stays dry. However, diesel is susceptible to moisture, which can lead to bacterial growth and the formation of sludge. So, if you notice any signs of discolouration or contamination in your diesel fuel, it's important to take action to prevent further degradation and potential engine problems.
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Clogged fuel filters
A clogged diesel fuel filter can cause serious issues for your engine. Fuel filters retain the contaminants they encounter, but they can become clogged over time. This can cause havoc for your engine, starving it of fuel and leading to breakdowns.
A clogged fuel filter will restrict fuel flow to your engine, leading to a host of noticeable symptoms. These include:
- Difficulty starting the engine
- Engine misfiring
- Rough idling
- Poor engine performance
- Lower fuel efficiency
- Hesitation upon acceleration
- Unusual noises, such as knocking or sputtering
- Increased emissions
Regular maintenance is essential to prevent these issues. Checking your fuel filter regularly and replacing it when necessary will ensure your diesel engine runs smoothly, extending its lifespan and saving you money in the long run.
A clogged filter can be cleaned by removing it, tapping out debris, spraying with a cleaner such as B-12 Chemtool, and letting it dry. If it is heavily clogged, it may need to be replaced.
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Engine performance issues
One of the most common signs of bad diesel is a decrease in fuel efficiency. If you find yourself refuelling more often despite normal usage, this could be an early warning sign of bad diesel.
Another indicator is rough idling, frequent stalling, or reduced power output. If your engine is struggling to start, or you experience sputtering or loss of power during acceleration, this could be due to bad diesel fuel.
In some cases, contaminated diesel fuel can shut down the engine completely. Water contamination, in particular, can lead to corrosive acids and biofilms that harm your engine, clog fuel filters, and affect performance. Water may enter the fuel tank through condensation, leaks, or even at the point of purchase. If you notice a cloudy or hazy appearance in your diesel fuel, this could indicate water contamination.
Other signs of contaminated diesel include black soot deposits on the exterior of your tailpipe, visible water in the fuel tank, or particles floating in the fuel.
If you suspect bad diesel fuel, it is important to take proactive measures such as using a good multifunction diesel additive with detergency to resolve the issue. Regular engine inspections and maintenance can also help identify and mitigate the impact of bad diesel.
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