How diesel gelling happens
Diesel fuel naturally contains paraffin wax. As the temperature drops, the wax starts to form crystals; the temperature where that begins is the cloud point. Colder still, the crystals can clog the fuel filter, which is the cold filter plugging point. Eventually the fuel can thicken until it won’t flow at all, the pour point. The result is hard starting, lost power, or an engine that stalls or won’t start.
Fuel sold in cold regions is usually winter-blended, but blends and timing vary from supplier to supplier. Fuel bought in a warmer area, or before the seasonal switch, may not be ready for a sudden cold snap.
Cold-weather checklist
- Read your owner’s manual first. Some engine makers have specific rules about fuel blends and additives.
- Change the fuel filter on schedule, and before winter if it’s close to due. A partly clogged filter plugs sooner once wax starts forming.
- Drain the water separator regularly. Water in diesel can freeze and ice up the filter.
- Keep the tank fuller in winter, so there’s less room for condensation.
- Fill up at busy stations in your area during cold months, so you’re more likely to get fuel blended for the season.
- Use the block heater if your engine has one, as the manual directs.
- Treat the fuel before the cold arrives if you use an anti-gel additive. Follow the label; these products are generally meant to be added before fuel starts to gel.
- Don’t forget stored diesel. Farm, standby generator and equipment tanks need the same attention. Keep them clean and dry.
- Never add gasoline to diesel fuel, and don’t blend in other fuels unless your manual allows it.
If your diesel gels
Get the vehicle or equipment somewhere warm if you can, so the fuel and filter can thaw. A plugged filter often needs replacing. An emergency treatment made for gelled diesel may help; follow its label. If the engine still won’t run, call a qualified diesel technician. For engine oil for diesel pickups and trucks, see our diesel oil page.
Frequently asked questions
At what temperature does diesel fuel gel?
It depends on the fuel. AMSOIL notes that most fuels have a cloud point near 32°F (0°C), and that low-quality fuels may form wax crystals in temperatures as warm as 40°F (4°C). Winter blends are made to work at lower temperatures.
What’s the difference between #1 and #2 diesel?
#1 diesel is lighter and handles cold better. #2 diesel is the common year-round fuel and has more energy content. Winter blends often mix the two.
Can an additive fix fuel that has already gelled?
Standard anti-gel additives are generally meant to be added before fuel gels. AMSOIL makes a separate emergency product, Diesel Recovery, which AMSOIL says quickly dissolves gelled fuel and thaws frozen fuel filters.
AMSOIL diesel fuel additives for cold weather
- AMSOIL Diesel Cold Flow. AMSOIL says it “combats fuel gelling in cold weather,” “lowers cold filter-plugging point (CFPP) by up to 40°F (22°C),” “inhibits fuel-filter icing” and is “safe for use in all diesel fuels, including biodiesel.”
- AMSOIL Diesel 4-IN-1. AMSOIL says it “combines the benefits of AMSOIL Diesel Injector Clean, Diesel Cold Flow and Diesel Cetane Boost in one convenient package” and “provides excellent all-season protection and performance.”
- AMSOIL Diesel Recovery. AMSOIL calls it an “emergency fuel treatment for gelled diesel fuel” that “quickly dissolves gelled fuel” and “thaws frozen fuel filters.”
Product wording above is quoted or summarized from amsoil.com. Read each product’s label and data sheet for directions.
For engine oil and other fluids, use AMSOIL’s car and light truck lookup, heavy-duty on-road lookup or agriculture lookup, or start at AMSOIL’s official lookup guide.