When Does Diesel Gel? A Cold-Weather Guide
Cloud point, winter blends, additives and water: what actually stops diesel in the cold, and how to keep equipment, generators and fuel tanks running.
Diesel doesn’t gel at one set temperature. As No. 2 diesel cools, its natural paraffin wax starts to form crystals at the cloud point. Colder, the wax plugs fuel filters (the cold filter plugging point), and colder still the fuel stops pouring (the pour point). Every batch has its own numbers, which is why winter diesel is blended or treated for the season. Keep equipment running with winterized fuel, cold-flow additives added before the cold arrives, and water kept out of your tanks.
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01What diesel gelling actually is
Gelled diesel isn’t frozen. It’s wax coming out of the fuel.
No. 2 diesel naturally contains paraffin wax. When the fuel is warm, the wax stays dissolved. As it cools, the wax forms crystals, and the fuel goes through three stages, from warmest to coldest:
- Cloud pointThe first wax crystals appear and the fuel turns hazy. It’s the first warning sign, and the safest limit to plan around.
- Cold filter plugging point (CFPP)Enough wax has formed to clog a fuel filter. This is usually what actually stops an engine or a generator.
- Pour pointThe fuel has thickened so much it no longer flows. It won’t pump or pour, in the tank or in the lines.
There’s always a spread between cloud point and pour point, and every batch of fuel has its own numbers.
02So at what temperature does diesel gel?
There’s no single number. It depends on the batch, the season and what’s been blended in.
The U.S. diesel standard, ASTM D975, doesn’t set one cold-weather limit for the whole country. Instead, its appendix maps the expected low temperatures for each state and month, so suppliers can match winter fuel to where and when it’ll be used. That’s why diesel bought in July behaves differently from diesel bought in January.
What that means for you:
- Ask for the numbers. Before a cold snap, ask your supplier what the cloud point or CFPP of your winter deliveries is.
- Don’t run summer fuel into winter. Fuel that’s been sitting in a tank or generator since warm weather wasn’t made for January.
- Problems above freezing usually aren’t wax. If filters plug while it’s still in the 30s, look for water first (more on that below).
Fueling up before the cold?
We deliver off-road and on-road diesel to job sites, fleets, generators and tanks.
03Winter diesel: how blends and additives work
Winter diesel is regular No. 2 diesel that’s been blended with No. 1 diesel (kerosene), treated with cold-flow additives, or both.
No. 1 diesel and kerosene blends
No. 1 diesel, which is essentially kerosene, contains very little paraffin, so its cloud point is much lower. Blending it into No. 2 lowers the cloud point of the mix, and the more you blend in, the colder the fuel can go. For on-road engines, the kerosene has to be ultra-low sulfur. Follow your engine maker’s guidance on blending.
Cold-flow additives (anti-gels)
Cold-flow additives change how wax crystals form so they stay small enough to pass through filters. They work best added before temperatures drop, not after the fuel has started to cloud. There are also emergency products made to re-dissolve wax in fuel that has already gelled.
Don’t swap in a coarser filter
When filters keep plugging in the cold, it’s tempting to switch to a more porous filter. Fleet experts warn against it: the fix is the fuel and the water, not letting more debris through to the injectors.
04Biodiesel blends in the cold
Low blends behave almost exactly like regular diesel. Higher blends cloud a few degrees sooner.
According to the Clean Fuels Alliance America, citing the U.S. Department of Energy’s biodiesel handling guide, B5 (5% biodiesel) typically has about the same cloud point as straight No. 2 diesel. B20 can have a cloud point about 2 to 7°F higher. With the right additives and tank management, biodiesel blends run fine in winter.
We deliver B2 through B20 blends. If you run biodiesel, talk with us about which blend level makes sense for the coldest months. See biodiesel fuel.
05Water: the other winter problem
Water freezes at 32°F, well before diesel gels, and ice in the fuel causes problems that look like gelling.
Some water is almost always in diesel. It gets in through condensation, when warm fuel sits in a cold tank and moisture forms on the walls, and it settles to the bottom because it’s heavier than fuel. In winter it freezes in lines and filters and starves the engine.
- Keep tanks full. Less air space means less room for condensation.
- Drain water separators and tank bottoms on equipment and in the yard, especially as part of late-fall maintenance.
- Top off at the end of the shift, not the start, so equipment tanks sit full overnight.
06Cold-snap checklist for job sites and fleets
Most cold-weather fuel problems are prevented the week before the cold arrives.
- Get winterized fuel in the tank before the forecast drop. Additives and blends only help if they’re in the fuel before it gets cold.
- Burn down summer fuel. Don’t carry fuel from warm months into a January cold snap, especially in standby generators.
- Drain water from separators, equipment tanks and on-site storage tanks.
- Keep spare fuel filters on the truck or in the job trailer.
- Park out of the wind and use block heaters where you have them.
- Watch for the warning signs. Sputtering, power loss or hard starts in the cold usually mean a filter is starting to plug.
- Keep it safe. Never warm fuel lines, filters or tanks with an open flame, and never add gasoline to diesel.
On-site tanks see the same cold as your equipment. If you rent a tank from us, a SMART Tank reports its level so we refill before you run low, and keeping it topped off helps keep condensation down. See on-site fuel tank rentals and fuel management.
07Does heating oil gel too?
It can. No. 2 heating oil is a close cousin of No. 2 diesel, with the same kind of wax.
Tanks in a heated basement rarely have trouble. Outdoor above-ground tanks, and oil lines that run outside, are the ones at risk in a deep freeze. If your tank is outside, ask about a kerosene blend or an additive before winter, and keep an eye on the level: here’s how to read your oil tank gauge. See home heating oil delivery.
08Winter diesel FAQs
At what temperature does diesel gel?
There’s no single temperature. No. 2 diesel starts to form wax crystals at its cloud point, plugs filters a little colder at its cold filter plugging point, and stops flowing at its pour point. Each batch has its own numbers, which is why winter diesel is blended or treated for the season.
What’s the difference between cloud point and gel point?
Cloud point is when wax crystals first appear and the fuel turns hazy. “Gelling” usually means the fuel has gone further, to the point where wax plugs filters (the cold filter plugging point) or the fuel stops flowing (the pour point).
Does off-road diesel gel?
Yes. Off-road diesel is No. 2 diesel with red dye added for tax purposes, so it gels the same way on-road diesel does. It needs the same winter blending or additives.
Is No. 1 diesel better in winter?
No. 1 diesel has very little paraffin wax, so it handles cold far better than No. 2. Winter diesel is usually No. 2 blended with some No. 1 or kerosene, treated with cold-flow additives, or both.
Does biodiesel gel faster than regular diesel?
B5 typically has about the same cloud point as straight No. 2 diesel. B20 can cloud about 2 to 7°F higher. With the right additives and tank management, biodiesel blends run fine in winter.
How do you fix gelled diesel?
Warm the fuel system safely (move the equipment somewhere warmer, or use a block or fuel heater), use an emergency anti-gel product made to re-dissolve wax, and replace plugged filters. Never use an open flame, and never add gasoline.
Fuel for the cold months
We deliver off-road and on-road diesel, biodiesel blends, gasoline and DEF to job sites, fleets and facilities across PA, DE, NJ and MD, and we rent on-site tanks. As an essential business, we keep delivering through severe weather.
Sources
- Clean Fuels Alliance America, Cold Flow: Biodiesel, a Cold Weather Solution, citing the U.S. Department of Energy’s Biodiesel Handling and Use Guide (2023): cloud point, pour point, CFPP and B5/B20 cloud points.
- ASTM International, Work item WK95812, revision of ASTM D975: the standard’s appendix of 10th-percentile minimum temperatures by month.
- Heavy Duty Trucking, Keep Your Diesel Fuel from Freezing this Winter (Jim Park, 2020): paraffin and cloud point, kerosene blending, water in fuel, filter advice.
- Mansfield Energy, Fuel Troubles in the Cold? Here’s What to Do (January 2025): additive timing, re-liquefiers, water freezing at 32°F.
- Fuels, blends, delivery area, tank rentals and SMART Tanks: American Energy Supply.
American Energy Supply is a woman-owned, family-run fuel company in Upper Chichester, PA. Since 2009 we’ve delivered diesel, gasoline and DEF to job sites, fleets and facilities, and heating oil to homes across Delaware County, Chester County and New Castle County, DE. WBENC certified, PA Small Diverse Business and PA COSTARS member.
