What Temp Does Diesel Gel? #2 Starts Waxing at 6–14°F

Diesel gel temperature chart: what happens as it gets colder

Diesel doesn't freeze like water. It contains paraffin wax that stays dissolved while the fuel is warm. As fuel cools, the wax comes out as crystals, first as haze, then as a mesh that clogs filters, then as a gel that won't pour. The middle column follows a typical untreated #2 with a 14°F cloud point (Cenex's figure). Your fuel's numbers will be different, but the order is the same.

CFPP and pour-point rows apply the published offsets (Power Service, Chevron) to a 14°F cloud point. They are illustrations, not specs. Treated fuel and biodiesel blends behave differently; see the fuel-by-fuel table below.

Cloud point vs CFPP vs LTFT vs pour point

"Gel point" isn't a lab test. When people say it, they usually mean the pour point. Four tests describe how diesel behaves in the cold, and they give four different temperatures for the same fuel:

Test descriptions from ASTM D975-24 Appendix X5 and Chevron's Diesel Fuels Technical Review.

Which one actually predicts filter plugging?

ASTM D975 summarizes a 1981 Coordinating Research Council field test of cars and heavy trucks, and notes that no independent data has been published since. The findings:

• For untreated fuel, use cloud point. It came closest to a fail-safe predictor for every vehicle tested. Field work shows cloud point is a fair indication of the operability limit for fuels without cold-flow additives.
• For treated fuel, LTFT is the better guide. It predicted the flow-improved fuels most accurately, and later industry studies (not independent, ASTM notes) supported it for North American heavy-duty trucks.
• CFPP and pour point overpredict. Both said vehicles would run colder than many actually did. D975 warns that CFPP results more than 18°F (10°C) below the cloud point should be viewed with caution.
• No single test fits every fuel and every vehicle. Filter plugging depends on wax-crystal size and shape and on the fuel system (filter location, return-fuel heating), not just on the fuel (Chevron).

In practice: if nobody has treated the fuel, plan around the cloud point. If it's been treated with a flow improver, ask for the CFPP or LTFT, and be skeptical of a CFPP far below the cloud point.

What temperature each type of diesel gels at

Sources disagree on #2, partly because "#2" covers summer and winter fuel from many refineries. NREL gives −31°F to 23°F for diesel fuels in general. Take the ranges as typical, not guaranteed, and get the measured number for your load.

How cold will your fuel get? ASTM D975's state-by-state guide

ASTM D975 doesn't set a cloud point for diesel. It says it's unrealistic to guarantee operation in every condition and leaves cold-flow limits to agreement between supplier and buyer. What it does give is Appendix X5: tenth-percentile minimum temperatures for every state (some split by latitude or longitude) for October through March, built from 15–21 years of hourly readings at 345 weather stations.

The tenth-percentile minimum is the temperature the daily low falls below about 10% of the time, roughly 3 days in a 30-day month. Suppliers use it to set winter blends by region and month, which is why January diesel in Minnesota isn't the same fuel as January diesel in Georgia. January examples:

ASTM D975-24 Table X5.1 (°C, converted and rounded). Third column applies Cummins' 11°F margin and is an illustration, not an ASTM requirement.

How to use it: find your state and the coldest month you'll run, subtract a margin, and compare the result with the cloud point (or, for treated fuel, the CFPP or LTFT) your supplier quotes. By this measure, untreated #2 at 6–14°F only covers January in the warmest zones. D975 also lists what makes it worse: high elevation, unusual cold snaps, fuel moving between regions, and long shutdowns. And remember that 10% of nights are colder than the table.

Wind chill doesn't gel diesel. A cold night does.

Wind chill describes heat loss from skin. The National Weather Service says its only effect on objects like car radiators and water pipes is to make them cool faster. They don't get colder than the air. At −5°F with a −31°F wind chill, a fuel tank bottoms out at −5°F. Use the air temperature, not the wind chill, when you compare against a cloud point.

What wind does change is how fast you get there, and parked equipment gets there quickly. In the CRC field test cited by ASTM D975, 30% of vehicles ended the night with fuel within about 4°F (2°C) of the overnight low. The LTFT cools its samples at 1.8°F an hour precisely to copy a truck tank sitting overnight with the engine off.

A running engine is different. Many diesels send warmed excess fuel back to the tank, which heats it (Chevron). That's why the fuel that gels is usually in equipment that sat: a loader parked on a jobsite over a weekend, a truck parked over a holiday, or a standby generator with an outdoor tank that hasn't run in weeks.

Signs your diesel is starting to gel

• Hazy fuel. Cloudiness in a sample jar or a clear filter bowl means you're at or below the cloud point. Haze can also be water, so check for a water layer too.
• Hard start or no start after a cold night, especially on equipment that sat with the engine off.
• Starts, then stalls or loses power under load. The filter loads up with wax as fuel flows through it.
• A new filter fixes it, briefly. Cummins' test: if a fresh filter lets the engine run normally even for a short while, something in the fuel is plugging it.
• Fuel won't drain or pump from a tank or line. That's the pour point.

Wax or ice? Cummins' shop test: bring the plugged filter inside, drain it, set it upside down on paper and let it warm to room temperature. Ice melts and runs out as water. Most petroleum wax won't melt at room temperature. Ice means a water problem; wax means the fuel isn't rated for the cold.

Diesel already gelled? What to do

1. Warm the fuel, not just the engine. Move equipment into a heated building if you can. Wax doesn't redissolve the moment you pass the cloud point: Cummins says it takes warming to roughly 20–40°F above the fuel's CFPP. Never use an open flame on a fuel system.
2. Change the fuel filter. Wax caught in the filter often stays there, even at room temperature. Carry spares in winter.
3. Use a product made for gelled fuel, not a regular anti-gel. Flow improvers only work if they're mixed in before wax forms (Chevron). Emergency products such as Power Service Diesel 9-1-1 are sold to reliquefy gelled fuel; follow the label.
4. Fix the fuel before the next cold night. Once it's flowing, blend or treat it for the temperatures ahead. Otherwise it gels again.

The full step-by-step for trucks, equipment and storage tanks is in how to prevent diesel gelling.

Preventing gelling, in short

• Know your number. Ask for the cloud point and CFPP of each winter load. A lab fuel test can measure the cloud point of fuel already in a tank.
• Switch before the cold. Additives and #1 have to go in while the fuel is still above its cloud point (Chevron, Cummins).
• Winterize stored fuel too. A tank filled in summer still holds summer fuel in January.
• Don't double-dose. Cummins warns that too much additive can itself plug filters. Ask whether the fuel is already treated.
• Keep water out. Water turns to ice at 32°F, well before wax becomes a problem.

Details on each step: how to prevent diesel gelling.

Winter diesel matched to your coldest night

FuelGo delivers dyed off-road and clear on-road diesel and R99 renewable diesel nationwide, matched to your engines and how you're taxed, including winter blends. We also offer 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, delivered into site tanks, generators and equipment, or straight into trucks with mobile fleet fueling.

Not sure what's in a tank? Lab fuel testing checks cloud point along with water and contamination, and fuel polishing and tank cleaning deal with what it finds. Dispatch runs 24/7/365: get a free quote or call 800-720-4546. A dispatcher replies within the hour. Call before the first cold snap, not after a filter gels.

Diesel gel temperature FAQ

Sources: ASTM D975-24, Table 1 and Appendix X5 (NCWM copy) · ASTM D4539, Low-Temperature Flow Test · Chevron, Diesel Fuels Technical Review · Navistar IK1500074, Fuel Filters, Winter Additives and Blending Fuels for Cummins Engines · Detroit fuels brochure, cloud point · CHS, preparing diesel equipment for winter · Cenex, cold-weather diesel problems · Power Service, winter weather and diesel fuel · NREL, Biodiesel Handling and Use Guide (6th ed.) · Clean Fuels Alliance America, cold flow management · Neste MY Renewable Diesel product data sheet · Neste Renewable Diesel Handbook · National Weather Service, cold weather FAQ (wind chill)