The exact answer to how much water in a diesel tank is considered "bad" is anything exceeding the EN590 specification's maximum of 200 milligrams of water per kilogram of diesel fuel, equivalent to 200 parts per million (PPM). While a small amount of dissolved water is always present, exceeding this very low threshold significantly increases the risk of serious fuel system and engine problems.
Understanding Water Contamination in Diesel Fuel
Water contamination in diesel fuel is a critical issue that can lead to significant operational problems, costly repairs, and reduced engine lifespan. While the EN590 specification provides a clear maximum limit, even levels below this can cause long-term issues if not properly managed.
The EN590 Standard: Your Benchmark
The EN590 specification is the European standard for diesel fuel, outlining various quality characteristics, including the permissible level of water contamination. As per this crucial standard:
- Maximum Limit: EN590 states a maximum of 200 milligrams (mg) of water per kilogram (kg) of diesel fuel.
- PPM Equivalent: This translates directly to 200 parts per million (PPM).
This means that for every 1,000,000 parts of diesel fuel, no more than 200 parts should be water by weight. While 200 PPM might seem like an incredibly small amount, it is the biggest factor for causing problems in diesel fuel, as highlighted by the EN590 specification's focus on it. Anything above this threshold is considered detrimental and indicative of a problem requiring attention.
Why Is Water in Diesel Fuel So Detrimental?
Even minute quantities of water can wreak havoc on a diesel fuel system. Here's why water contamination is considered "bad":
- Corrosion: Water in contact with metal components of the fuel tank, lines, and injectors can cause rust and corrosion. This leads to component degradation and the release of abrasive particles into the fuel.
- Microbial Growth (Diesel Bug): Water is essential for the growth of microorganisms like bacteria, fungi, and yeasts, commonly known as "diesel bug." These microbes live at the fuel-water interface, forming slime and biomass that can:
- Clog fuel filters rapidly.
- Corrode fuel tanks and lines.
- Degrade fuel quality.
- Fuel System Component Damage: Water reduces the lubricating properties of diesel fuel, leading to increased wear on high-pressure fuel pumps and injectors, especially in modern common rail systems which operate at extremely high pressures and tight tolerances.
- Fuel Filter Clogging: Both free water (visible droplets) and emulsified water (tiny dispersed water particles) can clog fuel filters, leading to reduced engine performance, power loss, and even complete engine shutdown.
- Injector Damage: Water, being incompressible, can cause severe damage to injector tips if it passes through the fuel system, leading to cavitation and pitting. In freezing conditions, water can form ice crystals that block fuel lines or damage components.
- Reduced Fuel Efficiency: Contaminated fuel burns less efficiently, leading to decreased power output and higher fuel consumption.
Sources of Water Contamination
Understanding how water enters a diesel tank is crucial for prevention:
- Condensation: The most common source. Temperature fluctuations cause water vapor in the air (inside the tank) to condense on the tank's inner walls, particularly when the tank is not full.
- Poor Storage Practices: Improperly sealed fuel caps, vent lines, or storage containers allow rainwater or humidity to enter.
- Contaminated Fuel Delivery: Fuel can arrive already contaminated from suppliers due to issues in their storage, transportation, or dispensing equipment.
- Leaking Equipment: Faulty seals or leaks in the fuel system can allow external water ingress.
Identifying and Addressing Water Contamination
Early detection and proactive management are key to preventing severe damage.
- Regular Fuel Checks: Periodically check for water accumulation in the fuel tank, especially at the bottom where water settles.
- Water Separators: Most diesel engines are equipped with fuel-water separators. These should be drained regularly, often daily or weekly, depending on usage and environmental conditions.
- Fuel Filtration: Install and maintain high-quality fuel filters that can capture water (e.g., hydrophobic filters) and particulate matter.
- Biocides: If microbial growth is suspected or confirmed, appropriate biocide treatments can kill existing microbes, though tank cleaning may still be required to remove sludge.
- Tank Maintenance: Keep fuel tanks as full as possible, especially during periods of inactivity, to minimize air space for condensation. Ensure proper ventilation and sealing.
Understanding Water Levels and Their Impact
The following table summarizes the implications of different water contamination levels in diesel fuel:
| Contamination Level (Water in Diesel) | Impact | Action Required |
|---|---|---|
| Up to 200 mg/kg (200 PPM) | Acceptable according to EN590 specification. Minimal impact, generally considered within safe operating limits. | Regular monitoring, routine water separator draining. |
| Above 200 mg/kg (200 PPM) | Detrimental and considered "bad." Increases risk of corrosion, microbial growth (diesel bug), fuel filter clogging, injector wear, and fuel system damage. | Proactive draining of water separators, investigate source of ingress, consider fuel polishing or treatment. |
| Free Water (Visible Droplets/Layer) | Highly Detrimental. Indicates significant contamination, posing immediate risks to engine performance and longevity. Likely contains microbial growth. | Immediate action required: Drain water, filter fuel, use biocides, consider professional tank cleaning and fuel polishing. |
In conclusion, any water in a diesel tank beyond the very strict limit of 200 PPM as specified by EN590 is considered "bad" and can lead to a cascade of expensive and performance-impacting problems. Vigilance and proper maintenance are essential for maintaining fuel quality and engine health. For more detailed information on fuel quality standards, consult resources like EN590 fuel quality standards or reputable fuel testing laboratories.
