Before restarting a diesel that has been stored for a long time, inspect for water, sediment, sludge, microbial contamination, corrosion, leaks, and damaged filters. If fuel is questionable, test it or remove it rather than assuming an additive or a new filter will fix the problem. Clean the tank when contamination warrants it, replace filters with the correct parts, and prime the system only as the equipment’s current manual directs.
Why a stored diesel fuel system needs inspection
Water is a key concern. It can harm fuel-system components and, where water and fuel meet, support microbial growth. The resulting biological material, along with dirt, sediment, sludge, or corrosion debris, can clog filters and restrict fuel flow. DTNA’s 2024 fuel-storage guidance and Detroit Diesel storage guidance both call attention to water and contamination in stored fuel systems.
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A foul odor, visible slime, or cloudy-looking fuel can be a warning, but appearance alone does not establish the fuel’s condition. Perkins describes fuel assessment that can include visual inspection and analysis for water, particles, and microbial growth. If the fuel looks questionable or filters have repeatedly plugged, testing can help distinguish the problem before choosing a remedy.
Corrosion depends on the tank and materials
Detroit Diesel service guidance warns that galvanized steel tanks, lines, or fittings can react with fuel and create material that clogs filters. Check the equipment’s applicable manual and inspect for corrosion rather than assuming every tank uses the same materials.
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- RAPID-ACTING DEEP CLEAN: Concentrated diesel fuel system cleaner designed to work quickly on performance-robbing deposits to restore the fuel system
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- RESTORES DPF PERFORMANCE: Reduces deposit buildup to support a cleaner DPF and reduce regeneration frequency
- TURBO DEPOSIT CONTROL: Reduces deposit buildup that affects turbo response, supporting smoother acceleration and restored boost
The U.S. EPA reported that 83 percent of 42 underground storage tanks storing diesel in a 2016 study showed moderate or severe corrosion of metal components. EPA cautions that this sample does not establish a nationwide rate. It concerns underground storage tanks, not vehicle tanks or all diesel systems.
Identify the system and find its restart instructions
Record the equipment make, model, engine, and serial number, then locate its current operation and maintenance manual and any storage-restart procedure. Fuel-filter arrangements, separator designs, approved fuel, and priming methods vary. Perkins notes that fuel-pump and priming arrangements differ, so a procedure for one engine should not be assumed to apply to another.
Rank #2
- EASY ONE-BOTTLE USE (2-Pack Value): Includes two 12 oz bottles. Pour into the fuel tank and drive normally. Each bottle treats 30-40 gallons of diesel. Use every 5,000 miles or as needed
- RAPID-ACTING DEEP CLEAN: Concentrated diesel fuel system cleaner designed to work quickly on performance-robbing deposits to restore the fuel system
- CLEANS INJECTORS FAST: Removes injector deposits and restores spray patterns for smoother running, improved response, and more efficient combustion
- RESTORES DPF PERFORMANCE: Reduces deposit buildup to support a cleaner DPF and reduce regeneration frequency
- TURBO DEPOSIT CONTROL: Reduces deposit buildup that affects turbo response, supporting smoother acceleration and restored boost
Inspect before starting the engine
With the engine off, check accessible components without opening or dismantling parts unless the manual directs you to do so. Look for:
- Fuel leaks, loose or damaged lines and connections, and compromised tank seals.
- Visible corrosion, contamination around the fill opening, or damaged filters and separator bowls.
- Water, sediment, sludge, or other visible contamination in the accessible tank contents and water separator.
- Signs of repeated filter restriction or a history of fuel-related faults.
If the tank design permits safe sampling, take a representative sample using the equipment’s sampling procedure and a suitable container. Where practical, a sample from the tank bottom can help reveal water or settled material that is not apparent in fuel drawn from higher up. DTNA recommends inspecting for dirt, water, and sludge; Perkins lists visual checks and water and microbial analysis among fuel-assessment methods.
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- TWO-STEP FUEL SYSTEM RESET: Includes AR6400-D Diesel Fuel System Cleaner + AR6500 Diesel Treatment (40 oz) for a complete clean-and-maintain solution
- HOW IT WORKS: Use AR6400-D first for a deep clean (12 oz treats 30-40 gallons), then use AR6500 at every fill-up for ongoing protection (40 oz treats up to 400 gallons)
- FOR ALL DIESEL ENGINES: Suitable for all diesel vehicles and equipment, including modern HPCR systems
- CLEANS INJECTORS & RESTORES RESPONSE: Removes injector deposits and restores spray patterns for smoother running, improved response, and more efficient combustion
- IMPROVES LUBRICITY (ASTM D6079): AR6500 is tested to improve lubricity by 43% to protect fuel system components, including wear-sensitive parts like the CP4 pump
Choose whether to test, drain, filter, or clean
There is no universal age cutoff that proves diesel must be discarded after a particular number of months. Fuel blend, storage conditions, tank condition, and test results all matter. Match the remedy to what the inspection or analysis shows:
| Condition or uncertainty | Reasonable next step | Important limit |
|---|---|---|
| Routine water in the separator, with fuel otherwise acceptable | Drain the separator as the manual directs and service the filters if required. | This does not establish that the rest of the tank or fuel is clean. |
| Questionable fuel, suspected microbial growth, or recurring filter plugging | Arrange suitable fuel testing. Perkins describes assessment for water, visual condition, particles, biodiesel content, and microbial growth. | A visual check alone may not quantify fuel quality or identify the cause of recurring restriction. |
| Water or particulates in fuel that is otherwise suitable for treatment | Consider filtration or fuel polishing with equipment appropriate to the fuel and system. | Filtration may remove water and particulates, but does not necessarily remove tank deposits or repair corrosion. |
| Significant sludge, deposits, or established contamination | Remove contaminated fuel and clean the affected tank or system as appropriate; consider qualified service for large or inaccessible tanks. | A filter change or additive alone is not a substitute for removing contaminated fuel and deposits. |
Perkins and DTNA guidance supports condition-based assessment rather than a single remedy for every stored system. The appropriate service method depends on the tank, contamination, fuel volume, and equipment design.
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- COMPLETE FUEL SYSTEM CLEANER: Diesel Extreme works through your entire fuel system removing harmful deposits, water, and sludge while improving cetane for smoother, more efficient combustion.
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Remove water and contamination safely
Drain water and contaminated fuel using the method specified for the tank and machine. If contamination or sludge is established, clean the tank and remove deposits as appropriate; replace contaminated filters. A filtration unit may be suitable for some fuel and applications, but follow that unit’s operation manual and fuel limits. For example, the cited Fuel Service filtration-unit manual warns not to run its pump dry.
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Detroit Diesel storage guidance describes biocide treatment, but that is not a universal instruction to add biocide to every stored system. Use a biocide only if it is appropriate and permitted for the engine and fuel, and follow both the product label and engine-manufacturer advice. Treatment does not replace removing water, sludge, or contaminated fuel, or correcting the source of contamination.
Best Value
- EASY ONE-BOTTLE USE (2-Pack Value): Includes two 12 oz bottles. Pour into the fuel tank and drive normally. Each bottle treats 30-40 gallons of diesel. Use every 5,000 miles or as needed
- RAPID-ACTING DEEP CLEAN: Concentrated diesel fuel system cleaner designed to work quickly on performance-robbing deposits to restore the fuel system
- CLEANS INJECTORS FAST: Removes injector deposits and restores spray patterns for smoother running, improved response, and more efficient combustion
- RESTORES DPF PERFORMANCE: Reduces deposit buildup to support a cleaner DPF and reduce regeneration frequency
- TURBO DEPOSIT CONTROL: Reduces deposit buildup that affects turbo response, supporting smoother acceleration and restored boost
Dispose of drained fuel, water, used filters, and cleaning waste according to applicable local requirements. Tank-entry, chemical-cleaning, fire-safety, and waste-handling procedures depend on the actual equipment and contaminant; do not improvise them. Use the equipment manual, local requirements, or qualified service support.
Replace filters and restore the system
Fit the correct primary, secondary, or separator filter for the specific engine. Confirm fitment using the equipment serial number and current parts information rather than relying on a filter number from another model. Caterpillar’s filter-service guidance illustrates the general care needed: drain a separator if fitted, keep dirt out during service, install the correct filter, prime as prescribed, and check for leaks after starting. The exact parts and sequence remain equipment-specific.
Prime and restart according to the manual
- Complete the specified service. Confirm that contaminated fuel and affected components have been addressed and the correct filters are installed.
- Use the prescribed priming method. Follow the current operation and maintenance manual for the exact engine and pump arrangement. Perkins warns not to loosen high-pressure fuel lines to bleed air; fuel-system methods vary by engine.
- Start and check the equipment. Once the manual’s servicing and pre-start checks are complete, start the engine and inspect for leaks and warning indicators. Caterpillar’s filter guidance also calls for a leak check after starting.
- Stop if there is a problem. If a leak, abnormal restriction, or fault appears, stop and follow the service manual or obtain qualified help rather than continuing to run the engine.
For relevant Perkins equipment and fuel circumstances, Perkins storage-restart guidance recommends clean diesel and new filters. Where biodiesel has remained in the system for an extended period, it advises draining the tank, replacing filters, filling with clean diesel, and running the engine to clear biodiesel from the system. Treat this as Perkins guidance for the applicable equipment and context, not a universal procedure.
When professional help is the better choice
Seek qualified service if contamination is extensive, the tank is difficult to access, corrosion or component damage is visible, filters plug repeatedly, or the manual does not provide a safe procedure for the work required. Large or inaccessible tanks may require professional fuel polishing or tank cleaning. Do not enter a tank or use unverified cleaning chemicals based on generic advice.
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