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Introduction
When diesel-powered equipment sits idle for years, the fuel inside its tanks can undergo dramatic chemical changes. What was once clean, amber-colored diesel may transform into a thick, black, tar-like substance that clogs filters, coats fuel lines, and threatens injectors. This article explores the nature of old diesel fuel degradation, clarifies key terminology, and offers practical strategies for cleanup and prevention—enriched with field anecdotes and historical context.
What Is the Black Goo?
Operators have described the substance as one of the most stubborn materials they've ever encountered. It resists degreasers, hot water, and even pressure washing. Chemically, it may be:
An electrician in Minnesota revived a DT466E engine that had sat for six years. After draining the tanks, he discovered thick black goo coating the fuel system. Despite the engine running well initially, he feared long-term damage. He cleaned the tank using gasoline and a hot water pressure washer, then replaced filters and cleaned the strainer screen with carb cleaner. His concern shifted to the injectors and internal fuel passages.
Cleaning Strategies and Chemical Solutions
Operators have experimented with various methods to dissolve or remove the goo:
A Missouri operator treated his bulk diesel tank with biocide after discovering microbial contamination. The treatment killed the growth, but filters clogged rapidly as the dead biomass circulated through the system. He went through 2–3 filter changes before the fuel ran clean again. This highlights the importance of stocking extra filters during remediation.
Historical Insight: Renewable Fuels and Shelf Life
In Australia, renewable diesel fuels made from tallow (animal fat) have uncertain shelf lives. These fuels may degrade faster than petroleum-based diesel, contributing to sludge formation. Similar issues have been reported in North America with biodiesel blends, especially when stored in humid environments.
Best Practices for Dealing with Old Diesel
In Pennsylvania, a DT466 engine sat outside for 20 years. With two sets of jumper cables and no priming, it started and ran—despite the fuel being decades old. While not typical, this story underscores the resilience of some diesel engines and the importance of thorough cleanup before assuming the worst.
Conclusion
Old diesel fuel can become a formidable adversary, turning into black goo that resists conventional cleaning methods and threatens engine health. Whether caused by oxidation, microbial growth, or poor fuel quality, the solution lies in a combination of mechanical cleaning, chemical treatment, and preventive maintenance. With the right approach—and a few extra filters—operators can restore their machines and keep them running strong, even after years of dormancy. In the world of diesel, time may tarnish the fuel, but not the spirit of those who revive it.
When diesel-powered equipment sits idle for years, the fuel inside its tanks can undergo dramatic chemical changes. What was once clean, amber-colored diesel may transform into a thick, black, tar-like substance that clogs filters, coats fuel lines, and threatens injectors. This article explores the nature of old diesel fuel degradation, clarifies key terminology, and offers practical strategies for cleanup and prevention—enriched with field anecdotes and historical context.
What Is the Black Goo?
Operators have described the substance as one of the most stubborn materials they've ever encountered. It resists degreasers, hot water, and even pressure washing. Chemically, it may be:
- Asphaltenes: Heavy hydrocarbon molecules that precipitate out of diesel as it oxidizes.
- Oxidized Hydrocarbons: Resulting from long-term exposure to air and heat, forming sticky residues.
- Biological Contaminants: Microbial growth (often called “humbugs”) that thrive in water-diesel interfaces and produce sludge.
- Fuel Polishing: A process that filters and recirculates diesel to remove contaminants and restore usability.
- Biocide: A chemical additive that kills microbial growth in fuel systems.
- Fuel Strainer Screen: A mesh filter that traps large particles before fuel reaches the pump or injectors.
- DT466E: A popular International diesel engine known for durability but sensitive to fuel quality.
An electrician in Minnesota revived a DT466E engine that had sat for six years. After draining the tanks, he discovered thick black goo coating the fuel system. Despite the engine running well initially, he feared long-term damage. He cleaned the tank using gasoline and a hot water pressure washer, then replaced filters and cleaned the strainer screen with carb cleaner. His concern shifted to the injectors and internal fuel passages.
Cleaning Strategies and Chemical Solutions
Operators have experimented with various methods to dissolve or remove the goo:
- Gasoline Soaking
Effective at slowly dissolving the sludge, especially for screens and small components.
- Hot Water Pressure Washing
Useful for pushing residue around but not effective at breaking it down.
- Biocide Additives
Products like Power Service Bio Kleen can kill microbial growth and help clean fuel systems when mixed with fresh diesel.
- Fuel Polishing Services
Specialized trailers with kidney-loop filtration systems can clean bulk tanks and inspect solids removed.
- Sodium Hydroxide (Lye)
A strong alkali used in drain cleaners. Some operators tried soaking tanks with lye and water, but results were mixed.
A Missouri operator treated his bulk diesel tank with biocide after discovering microbial contamination. The treatment killed the growth, but filters clogged rapidly as the dead biomass circulated through the system. He went through 2–3 filter changes before the fuel ran clean again. This highlights the importance of stocking extra filters during remediation.
Historical Insight: Renewable Fuels and Shelf Life
In Australia, renewable diesel fuels made from tallow (animal fat) have uncertain shelf lives. These fuels may degrade faster than petroleum-based diesel, contributing to sludge formation. Similar issues have been reported in North America with biodiesel blends, especially when stored in humid environments.
Best Practices for Dealing with Old Diesel
- Drain and clean tanks thoroughly before refueling
- Use gasoline or solvent to dissolve stubborn residues
- Replace all filters and clean strainer screens
- Add biocide to fresh fuel and monitor filter clogging
- Consider fuel polishing for large tanks or sensitive equipment
- Inspect fuel lines and injectors for internal contamination
In Pennsylvania, a DT466 engine sat outside for 20 years. With two sets of jumper cables and no priming, it started and ran—despite the fuel being decades old. While not typical, this story underscores the resilience of some diesel engines and the importance of thorough cleanup before assuming the worst.
Conclusion
Old diesel fuel can become a formidable adversary, turning into black goo that resists conventional cleaning methods and threatens engine health. Whether caused by oxidation, microbial growth, or poor fuel quality, the solution lies in a combination of mechanical cleaning, chemical treatment, and preventive maintenance. With the right approach—and a few extra filters—operators can restore their machines and keep them running strong, even after years of dormancy. In the world of diesel, time may tarnish the fuel, but not the spirit of those who revive it.
