Diesel fuel polishing service for fuel that's been sitting too long.
Stored diesel picks up water, sediment and microbial growth while it waits. We polish it at your tank, so the fuel is ready to run on the day the generator or equipment actually needs it.
- Water and contaminants removed so stored fuel is ready to run
- Done at your location: technicians bring the equipment
- One-off cleanups or a regular maintenance plan
Get a fuel polishing quote
Tell us about the tank and what you're seeing. A dispatcher replies within the hour.
Prefer to talk it through? Call 800-720-4546, 24/7.
Diesel doesn't stay good just because nobody touched it
Diesel starts degrading within months. A tank that sits between generator tests, or holds reserve fuel for a season, is quietly collecting three kinds of problem.
Water
Temperature swings cause condensation inside the tank. Water is heavier than diesel, so it settles at the bottom, right where the pickup draws from, and it corrodes the tank while it sits.
Microbial growth
Bacteria and fungi live where fuel meets water, the "diesel bug." They form slime and sludge that plug filters and produce acids that attack tanks and fuel system parts.
Sediment & degradation
Over time diesel oxidizes and forms gums and particles. Rust and debris settle out too, then get stirred up when the tank is refilled or the engine starts drawing hard.
Why standby tanks are the worst affected
A generator that only runs for tests can hold the same fuel for a year or more. Modern ultra-low sulfur diesel, especially when blended with biodiesel, holds water more readily than the high-sulfur fuel older tanks were designed around. The contamination builds slowly and shows up all at once: the set starts, takes load, and the filters choke.
Signs your stored diesel needs polishing
If any of these sound familiar, the fuel is already costing you. Each one gets worse with time.
- Dark, hazy or cloudy fuel. Good diesel looks clear and bright in a sample jar.
- Water or sludge at the bottom. Visible when you sample or drain the tank.
- Filters clogging early. Changing filters well before their interval is a classic sign of microbial growth.
- Rough running under load. Surging, smoke or a struggle during load tests.
- Slime on filter elements. Dark mats or a slimy film point to biological contamination.
- Fuel that has sat untested. A year or more in the tank with nobody checking it.
What diesel fuel polishing actually does
Polishing circulates the fuel out of the tank, through filtration and water separation, and back in. It strips out free water, sediment, sludge and microbial debris so the fuel you already paid for can be used again. It cleans the fuel rather than replacing it.
| Option | What it does | When it fits |
|---|---|---|
| Fuel polishing | Filters and dewaters the fuel in place, without emptying the tank | Fuel is contaminated but still salvageable, or as routine maintenance |
| Tank cleaning | Removes sludge and buildup from the tank itself, usually with the tank emptied | Heavy sludge or microbial mats coating the tank walls and floor |
| Fuel replacement | Removes the old fuel and refills with fresh diesel | The fuel is too degraded to recover |
We do all three. Our crews polish the fuel, clean the tank itself of sludge, water and other contaminants, and pump the fuel out entirely when it can’t be saved.
Read more: fuel polishing vs. tank cleaning →
If polishing isn't enough, we'll say so
Some fuel is too far gone to recover. When that's the case we'll tell you straight, pump the old fuel out, clean the tank, and refill it with fresh dyed diesel, clear diesel or R99 renewable diesel on the same account.
How an on-site polishing visit works
The fuel stays where it is. We bring the equipment to the tank.
Lab testing before we touch the tank
Testing tells you whether stored diesel needs polishing before a symptom does. We pull a sample from the tank and send it to a lab that checks it for water, sludge, bacteria and more. The results decide what the tank needs. What the lab tests →
Pair it with deliveries
Polishing works best alongside a keep-full program. A full tank leaves less room for condensation, and scheduled fills keep fuel turning over. Generator fuel delivery →
What a diesel fuel lab test checks
We take a sample from your tank and send it to the lab. These are the most common diesel tests, and what each one tells you about the fuel.
| Test | Method | What it tells you |
|---|---|---|
| Appearance (clear & bright) | ASTM D4176 | A quick visual check for haze, free water and visible particles |
| Water & sediment | ASTM D2709 | How much free water and sediment has settled into the fuel |
| Water content (Karl Fischer) | ASTM D6304 | Total water in parts per million, including water you can’t see |
| Microbial growth | ASTM D7687 / D6974 | Bacteria and fungi (“diesel bug”), the cause of sludge and plugged filters |
| Particulate contamination | ASTM D6217 / ISO 4406 | Dirt, rust and solids that wear injectors and plug filters |
| Oxidation stability | ASTM D2274 | How fast the fuel is breaking down into gums and sediment as it ages |
| Cetane index | ASTM D976 / D4737 | Ignition quality: whether the engine will start and run cleanly |
| Flash point | ASTM D93 | Safety, and whether the diesel has been mixed with a lighter fuel |
| Cloud point & CFPP | ASTM D2500 / D6371 | How cold the fuel can get before wax plugs filters |
| Sulfur | ASTM D5453 | Whether the fuel still meets the 15 ppm ultra-low-sulfur limit |
Anyone whose fuel waits longer than it works
Data centers
Generator farms holding diesel that may sit a year between real starts, with uptime commitments riding on it.
Data center fuelingHospitals & critical facilities
Standby power that has to start and carry load the first time, every time.
Generator fuelingTelecom & tower sites
Remote generators that nobody visits between tests, where a clogged filter means a site down.
Telecom fuelingGovernment & military
Reserve fuel and generator farms held for emergencies that may not come for months.
Government fuelingFleets with on-site tanks
Yard storage where water and sediment end up in truck fuel systems and injectors.
Fleet fuelingBulk & seasonal storage
Large tanks filled ahead of a season or held as reserve, where fuel turnover is slow.
Bulk fuel deliveryPolish once, or keep it clean all year
A one-off polish fixes the fuel you have. A plan keeps it from going bad again.
Single polishing visit
For a tank with a known problem, fuel that has sat for an unknown time, or a site preparing for storm season.
- Quote before the visit
- Polished on site at your tank
- Refill with fresh fuel if needed
Regular maintenance plan
Scheduled polishing that keeps stored fuel in condition year-round, so you prevent problems instead of finding them.
- Visits on a set schedule
- Combined with keep-full deliveries
- Tank monitoring available
Between visits: how to slow contamination down
Keep tanks full to limit condensation, drain water from the bottom regularly, turn fuel over rather than letting it sit for years, and keep tank vents and fill caps sealed. Read how long diesel lasts in storage and how water in diesel damages engines.
Diesel fuel polishing questions
What is diesel fuel polishing?
Fuel polishing circulates stored diesel through filtration and water separation and returns it to the tank. It removes water, sediment, sludge and microbial debris so the existing fuel is usable again, without replacing it.
How is fuel polishing different from tank cleaning?
Polishing cleans the fuel in place. Tank cleaning removes sludge and buildup from the tank itself, usually with the tank emptied. Polishing suits fuel that is contaminated but salvageable and routine maintenance; heavy buildup on the tank walls calls for cleaning.
Do you clean fuel tanks?
Yes. Along with polishing the fuel, we clean the tank itself of sludge, water and other contaminants. If the fuel can’t be recovered, we pump it out and refill the tank with fresh fuel on the same account.
What does a diesel fuel test check?
We pull a sample from your tank and send it to a lab. Common diesel tests check appearance, water and sediment, water content (Karl Fischer), microbial growth, particulates, oxidation stability, cetane index, flash point, cloud point and sulfur. The results tell us whether the fuel needs polishing, the tank needs cleaning, or the fuel needs replacing.
Do you polish fuel at our site?
Yes. Polishing is done at your location. Our technicians arrive with the equipment and polish the fuel in your tank, at a time scheduled around your operations.
How often should stored diesel be polished?
It depends on how long fuel sits, the climate and the condition of the tank. Many facilities test stored fuel at least once a year and polish when the results or the symptoms call for it. A maintenance plan puts polishing on a set schedule.
Can polishing save diesel that has gone bad?
Often, yes, if the fuel is contaminated with water, sediment or microbial growth but hasn't degraded too far. If it can't be recovered we'll tell you, and we can refill the tank with fresh fuel.
What causes diesel fuel contamination?
Mostly condensation, which puts water in the tank, followed by microbial growth at the fuel and water interface. Oxidation, rust and debris add sediment over time. Fuel that sits for months is the most at risk.
Can you refill the tank after polishing?
Yes. We deliver off-road dyed diesel, on-road clear diesel and R99 renewable diesel, so the tank can be topped up on the same account.
How do I keep stored diesel from going bad?
Keep the tank full, drain water from the bottom, turn the fuel over regularly, keep vents and caps sealed, and test it periodically. Monitoring and a regular polishing plan take most of the guesswork out.
Find out what's in the tank before the generator does.
Tell us the tank, the fuel and how long it's been sitting. A dispatcher replies within the hour with a quote and a time.
Or email [email protected]