How to Prevent Diesel Gelling and Fix It When It Happens
Buy winter fuel rated below your coldest night, and add anti-gel while the fuel is still above its cloud point. Then keep water out and heat on the equipment that sits.
To prevent diesel gelling, run winterized fuel whose cloud point is below the coldest temperature it will see, and add anti-gel while the fuel is still above its cloud point, right before you fill so it mixes. Keep water out, keep parked equipment and filters warm, and carry spare filters.
Anti-gel can't fix fuel that has already gelled. That takes heat (Cummins: warm the fuel 20–40°F above its cold filter plugging point), an emergency reliquefier and new filters. Never use an open flame. For gel temperatures by fuel, see what temp does diesel gel?
How to prevent diesel gelling: what to do, and when
Diesel gels because paraffin wax comes out as crystals once the fuel drops below its cloud point, about 6–14°F for untreated #2. Every fix has to happen before that point. The tests and the numbers for each fuel are in our gel temperature guide. This page is the plan.
| When | What to do | Why |
|---|---|---|
| Early fall, before the first frost | Drain water from tanks and separators, change fuel filters, clean pump screens. Find out the cloud point of fuel already in storage. Agree on a winter spec with your supplier. | Cenex's winter checklist for aboveground and underground tanks starts here. Water freezes at 32°F, long before wax shows up. |
| Overnight lows near 30–32°F | Switch deliveries to winter fuel. Start treating each fill with anti-gel. Blend storage tanks down with #1 now. | Cenex and CHS switch at about 30–32°F. Power Service starts treating below 30°F. Cenex wants fuel 10–15°F above its cloud point when you blend. |
| Lows of 20°F and below | Run winterized premium fuel. Plug in heaters on anything parked outside. | Cummins treats 20°F and below as winter operating conditions and recommends premium diesel there. |
| Before a cold snap | Compare the forecast low with your fuel's cloud point. Top off with winter fuel while the tank is still warm. Move equipment indoors or out of the wind. | Cummins wants the cloud point at least 11°F below the lowest temperature the fuel will see. Additives and #1 only work if they go in before wax forms. |
| Every day in winter | Drain water separators. Fill tanks at the end of the shift. Plug in block and filter heaters. Check filter bowls for haze. | Full tanks hold less moist air to condense. A waterlogged filter can swell and freeze (Cenex). |
Timing guidance from Cenex, CHS, Power Service and Cummins (see sources). How cold your state gets by month is in the ASTM D975 regional table.
By situationPrevention by situation: fleets, job sites, generators and farm tanks
A truck that runs all day rarely gels. Most diesel engines send warmed excess fuel back to the tank, which heats it (Chevron). The fuel that gels is the fuel that sits. That's why the plan depends on how your equipment is used.
Trucks parked overnight and over weekends
- Watch fuel bought elsewhere. ASTM D975 lists movement between regions as a cold-flow risk. A tank filled in a warm state carries that state's cloud point north. Top off with local winter fuel or treat it before the cold run.
- Heat the filter. Navistar notes coolant-heated filters are the most effective.
- Fuel in the yard. Overnight mobile fleet fueling fills trucks with seasonal fuel and leaves full tanks for the cold night.
Equipment that sits outside
- Fill at the end of the shift, not the morning. A full tank holds less moist air.
- Park out of the wind, or in a building. Wind doesn't make fuel colder than the air, but it gets it there faster.
- Dyed fuel needs winterizing too. Off-road diesel gels like clear diesel, and site tanks filled in fall often hold unwinterized fuel.
- Keep spare filters and a reliquefier in the service truck.
Outdoor tanks that turn over slowly
- Know what's in the tank. A tank filled in summer still holds summer fuel in January. Test its cloud point in the fall.
- Treat or blend in the fall, while the fuel is warm. Waiting until it's cold means the additive won't mix.
- Underground tanks are safer. Cenex puts underground temperatures at 35–45°F, above most cloud points. Aboveground and sub-base tanks track the air.
- Keep it full. See generator fuel delivery.
Mind the heel when you blend down
- Count the #2 already in the tank. Cenex's example: a 2,000-gallon tank holds 700 gallons of #2. Adding 700 gallons of a 50/50 blend leaves you at about 71/29, not 50/50. To get there, bring in 700 gallons of straight #1.
- Drain water and change dispenser filters before winter, and clean pump screens.
- Protect pumps, lines and dispensers with approved heating and insulation (NREL).
Buying winter diesel: what to ask your supplier
"Winter diesel" isn't a separate grade. It's #2 diluted with #1 (each 10% of #1 lowers the cloud point about 3°F), treated with cold-flow additives, or both. Blend ratios by temperature are in our winter blend guide. What matters when you order:
- Ask for numbers, not a name. Get the cloud point and the CFPP (or LTFT) of the fuel you're buying. Detroit and Cenex both say cold-flow additives do little for cloud point and that blending with #1 is the way to lower it. So a treated fuel can show a good CFPP with a cloud point that has barely moved.
- Ask whether it's already treated. Cummins says many commercial winter fuels already carry a winter additive, so ask before adding more.
- Match it to your coldest night. Cummins wants the cloud point at least 11°F below the lowest temperature the fuel will see. For generators and emergency equipment, use that margin.
- Switch before the cold, not during it. Cenex warns that wax crystals that form in a cold snap can stay even after you blend, and recommends an early move to winter fuel.
- The old fuel is still there. New winter fuel mixes with whatever #2 is already in the tank. Unless you account for the heel, the tank ends up warmer-rated than you paid for.
- Keep dyed and clear separate. Winterizing doesn't change the tax rules. Don't top up a road truck with dyed #1 (see dyed #1 and #2).
Diesel anti-gel additives: how to use them so they work
Anti-gel (cold-flow improver, wax crystal modifier) doesn't remove wax. Its polymers change the size and shape of wax crystals as they form, so they pass through the filter instead of matting on it (Chevron). That mostly lowers the CFPP and pour point. It does little for the cloud point. Seven rules:
- Add it while the fuel is above its cloud point. Chevron: additives must be blended in "before any wax has formed." Power Service and Howes say the same. For storage tanks Cenex wants the fuel 10–15°F above its cloud point. Added to cold fuel, the additive can settle out and end up on the filter.
- Pour it in before you fill. Howes says to add anti-gel right before fueling so the incoming fuel mixes it. In a storage tank, add it as the tank fills, or have the supplier blend it in at delivery.
- Dose for the temperature on the label. Many labels list a standard dose and a stronger one (often double) for temperatures below 0°F or for biodiesel blends. Products differ, so read yours.
- Don't overdose or double-dose. Cummins warns overuse can plug fuel filters and shorten aftertreatment life, and Detroit warns against excessive use. Howes says over-treating its own product isn't harmful. Follow your additive's label, and ask whether the fuel is already treated.
- Treat every fill. Untreated fuel added later dilutes the dose. Howes recommends treating at each fill-up once temperatures near freezing.
- Know the limit. Cummins calls additives "not a cure all": results depend on the fuel, and severe cold can call for fuel heaters as well. Chevron says no additive works equally in every fuel. Cenex adds that ULSD is harder to treat than older diesel.
- Anti-gel isn't a rescue product. Power Service says its emergency product, Diesel 9-1-1, "does not prevent fuel gelling," and its anti-gel can't reliquefy gelled fuel. You need both, for different jobs.
Power Service says treated fuel usually won't plug filters until 20–25°F below its cloud point. Chevron's typical CFPP gain is 25–35°F. Cenex says not to count on cold-flow improvers for more than 15°F below the cloud point. Plan on the conservative figure for equipment that has to start, and ask for the treated fuel's CFPP or LTFT.
Heat, shelter and water control
Block and coolant heaters
They keep the engine and coolant warm for starting (DOE). They don't warm the fuel tank. A diesel-fired coolant heater uses about 0.04–0.08 gallon an hour, against 0.6–1.5 for idling (DOE).
Fuel filter heaters
Cummins calls heating fuel just before the filter "an excellent method" of preventing plugging. To work, the heater must raise fuel 20–40°F above its CFPP at full fuel flow, not just at the rate the engine burns it.
Heated tanks, insulated lines
Equipment built for extreme cold has heated tanks, insulated lines and heated filters (Cummins). Insulation and tank blankets slow cooling but add no heat, so over a long freeze, pair them with a heater. Use approved heating equipment only.
Indoors, or out of the wind
A heated building is the best protection there is. Outside, Cummins notes that moving filters and lines out of the wind and road splash helps keep them warm.
Full tanks, drained separators
Tanks pull in humid air as fuel is drawn down, and it condenses (Cenex). Keep them full and drain water separators often in winter. Ice plugs a filter at 32°F, well before wax. See water in diesel.
Change before winter, carry spares
Start the season with fresh filters (Cenex). Cummins notes a larger filter, or filters in parallel, hold more wax before power drops off. Wax trapped in a filter often won't melt at room temperature, so carry spares.
Biodiesel blends and R99 renewable diesel in winter
- B20 clouds 2–7°F higher than the #2 it's blended into (Clean Fuels Alliance). NREL says to store blends 5–10°F above their cloud point.
- Additives do less in biodiesel blends. NREL says cold-flow additives are believed to work only on the diesel portion. Power Service doubles its dose for biodiesel blends, and Cenex adds an extra 10% #1 when blending down a biodiesel tank.
- R99 needs the right seasonal grade, not more additive. Neste says cold-flow additives give only minor improvement in its renewable diesel, and its CFPP sits close to its cloud point. Ask for the cloud point of the winter grade. R99 isn't at every terminal; where it can't be pulled locally it ships by rail or barge, so order winter supply early. See R99 renewable diesel.
Diesel already gelled? Step by step
- Confirm it's wax, not ice. Cummins' test: put in a new filter. If the engine runs, even briefly, something in the fuel is plugging it. Take the old filter into a warm shop, drain it, set it upside down on paper. Ice melts and runs out as water; most petroleum wax won't melt at room temperature. Ice means a water problem.
- Get heat to the fuel, safely. Move the equipment into a heated building if you can, or warm the tank, lines and filter with approved heaters. Never use a torch or open flame on a fuel system (Howes). Cummins says wax redissolves only when the fuel is warmed about 20–40°F above its CFPP.
- Use a reliquefier, not anti-gel. Emergency products are dosed into the tank and the filters. Power Service's 9-1-1 directions, for example: add it to the tank (16 oz per 20 gallons on the current label), fill the filters with half 9-1-1 and half diesel, reinstall, start, and idle to warm the fuel system. Follow your product's label.
- Replace the filters. Wax caught in the media often stays there, even after the fuel flows.
- Winterize before the next cold night. Once the fuel is liquid and above its cloud point, treat it with anti-gel or blend in #1. Otherwise it gels again. Running the engine helps too: return fuel warms the tank.
- Call for help with tanks you can't move. A gelled storage or generator tank, or one full of summer fuel with the cold still ahead, may be better pumped out and refilled with winter fuel, or polished and tested if it's also wet.
How long does thawing take? No engine maker publishes a time. It depends on how much fuel there is and how much heat reaches it. Go by temperature, not the clock: the fuel has to get 20–40°F above its CFPP. A full tank in a heated shop takes far longer than a filter.
MythsGelling myths: gasoline, kerosene, alcohol and idling all night
| Claim | Verdict | What the sources say |
|---|---|---|
| "Add a splash of gasoline" | No | Cummins: never mix gasoline into diesel; it can cause a fire or explosion. 20% gasoline only lowers the cloud point about 7°F and cuts viscosity, cetane and flash point. Chevron: 1% gasoline or less drops the flash point below the diesel spec. |
| "Cut it with kerosene" | Yes, within limits | Diluting #2 with #1 or kerosene is how winter blends are made (Chevron, Cummins). Add it before wax forms. The blend must still meet the engine's spec (Cummins: viscosity at least 1.3 cSt, cetane 45 below 32°F). K-1 kerosene allows 400 ppm sulfur, too much for DPF and SCR engines. On-road use is taxed. See #1 diesel vs kerosene. |
| "Pour in alcohol or gas-line antifreeze" | No | Cummins: alcohol in diesel is a fire and explosion hazard, and alcohol dilution raises the cloud point. The small amounts of de-icer built into some diesel additives are a different thing (Chevron). |
| "Just idle it all night" | Costly | A running engine does warm its tank with return fuel (Chevron). But a heavy truck burns about 0.8 gallon an hour idling (DOE). Cummins warns long idling with cold coolant dilutes the oil and builds carbon, and many states and cities restrict idling. A coolant heater and winter fuel cost less. |
| "Anti-gel will fix gelled fuel" | No | Anti-gel only works if it's in the fuel before wax forms (Chevron). Gelled fuel needs heat or a reliquefier. |
Winter diesel delivered before the cold
FuelGo delivers dyed off-road and clear on-road diesel and R99 renewable diesel nationwide, including winter blends, plus winter blending and additive packages for tanks and equipment that sit outside. That's 20 to 4,400 gallons per drop, and transport loads up to 7,500 gallons, into site tanks, generators and equipment, or straight into trucks with mobile fleet fueling. A keep-full program for generators and tank monitoring on bulk tanks help keep tanks topped up through the winter.
Not sure what's in a tank? Lab fuel testing checks cloud point along with water and contamination. Fuel polishing, tank cleaning and fuel pump-out deal with what it finds. When a cold snap catches you short, emergency fuel delivery runs 24/7/365. Get a free quote or call 800-720-4546. A dispatcher replies within the hour.
Common questionsDiesel gelling prevention FAQ
How do you keep diesel from gelling?
When should I add anti-gel to diesel?
Can you add anti-gel after diesel gels?
Does idling prevent diesel from gelling?
Can I add kerosene to diesel to prevent gelling?
Can you put gasoline in diesel to stop it gelling?
How do you unfreeze gelled diesel?
How long does it take for gelled diesel to thaw?
Sources: Navistar IK1500074, Fuel Filters, Winter Additives, and Blending Fuels for Cummins Engines · Cummins Service Bulletin 3379001, Fuels for Cummins Engines · Chevron, Diesel Fuels Technical Review · Detroit fuels brochure, cloud point · Cenex, 2023 Winter Fuels Products & Best Practices for Handling · Cenex, cold-weather diesel problems · CHS, preparing diesel equipment for winter · Power Service, winter weather and diesel fuel · Power Service, Diesel Fuel Supplement · Power Service, Diesel 9-1-1 · Howes, anti-gel: how and when to use it · Howes, how to keep diesel from gelling · NREL, Biodiesel Handling and Use Guide (6th ed.) · Clean Fuels Alliance America, cold flow management · Neste Renewable Diesel Handbook · U.S. DOE, idle reduction for heavy-duty trucks · ASTM D975-24, Appendix X5 (NCWM copy)