Winter diesel: blends, gelling and the seasonal premium

Winter diesel is ordinary diesel that has been blended or treated so it keeps flowing when the temperature drops. Diesel has paraffin wax in it, and below a certain point that wax starts to crystallize. If enough forms, the fuel gels and stops passing through the filter, and a truck that will not draw fuel does not move. That is why diesel at a northern pump changes through the winter and tends to cost a little more than the summer fuel.

How cold diesel can go

Three temperatures describe how a diesel handles the cold: the cloud point, where wax crystals first appear; the cold filter plugging point, the CFPP, where enough wax has formed to block a filter; and the pour point, where the fuel sets into a gel. Diesel gel temperature defines each one, names the test behind it and charts the published figures for number 2, number 1, winter blends and biodiesel. For this guide the point is that each temperature belongs to a particular batch of fuel, so the operable temperature is a property of the fuel, not a fixed line.

Number 2 versus number 1

Number 2 diesel is the standard on-road fuel, energy-dense but relatively waxy. Number 1 diesel is a lighter, kerosene-like fuel with far less wax and a much lower gel point, so it stays liquid in much colder weather. Winter fuel at a northern pump is usually a blend of the two, cut with more number 1 as the climate gets colder, sometimes with cold-flow additives on top to lower the operable temperature further. The colder the region and the season, the more number 1 goes into the mix.

Cold-flow improver additives reshape the wax crystals so they slip through a filter at a lower temperature than they otherwise would, which lets a blender hit a cold rating with less number 1 and its energy penalty. In the far north in deep winter, fuel can run heavy on number 1 or close to straight kerosene. Southern diesel skips almost all of this, which is part of why a southern pump and a northern pump can sell noticeably different fuel under the same word.

Basic, standard and premium winter diesel

Pull into a truck stop in January and the pump may offer more than one diesel: a base fuel, sometimes a middle grade, and something sold as premium. Those words come from the seller, not from a fuel standard. ASTM D975, the American specification for on-road diesel, defines grades by fuel type and sulfur level, number 1-D and number 2-D among them, and it sets no basic, standard or premium tier. It does not define a winter grade either. Cold-weather performance in the American spec is handled by agreement: buyer and supplier settle on a cloud point or cold filter plugging point suited to the location and the month, with the standard supplying tenth-percentile low-temperature charts by state and month as the reference.

Other countries do it the other way around. Canada's national diesel standard and Europe's EN 590 both write winter classes into the specification itself, keyed to a measured cold-flow temperature, so a class letter or number there is defined by the standard. That is part of why the vocabulary travels, and why the same word on a pump can mean different things on either side of a border.

What each tier usually means at the pump

Basic winter diesel is the seasonally adjusted number 2 that most stations sell as plain diesel. The terminal has cut it with some number 1, usually treated it with a cold-flow additive, and aimed at whatever operability temperature the region expects that month. Nothing on the pump claims more than the local seasonal spec, and in an ordinary winter that is the fuel almost every truck burns.

Standard winter diesel, where a chain sells a middle grade, is generally the same idea pushed further: a deeper number 1 cut, a heavier additive dose, or both, rated for a lower temperature than the base fuel. This is the point at which a seller may publish an actual number, a cold filter plugging point or a stated operability rating, on the pump or in a fuel spec sheet. Without a published number, the tier tells you the fuel was treated but not how far down it will go.

Premium winter diesel is the one tier where the word can carry a legal definition. A number of states enforce the premium diesel definition written by the National Conference on Weights and Measures, which sets floors a fuel has to clear before a pump may be labeled premium: a cetane number of at least 47, against the ASTM minimum of 40, along with requirements for low-temperature operability, thermal stability and lubricity. Most of that list is about combustion, injector cleanliness and how the fuel holds up in storage. Cold flow is one item on it. In a state that has not adopted the definition, premium means whatever the seller says it means.

Reading the tiers against the cold numbers

Every tier is still number 2 diesel blended down with number 1, treated with cold-flow improver, or both. Moving up a tier buys a lower cloud point and a lower cold filter plugging point, paid for with more kerosene or more additive. No separate winter chemistry appears at the premium pump.

Two things follow from that. A tier name is not a temperature: the operable temperature belongs to the specific fuel in that tank on that day, which is why a seller making a cold claim states a number for it. And a premium grade priced several cents over the base at the same station sits above the DOE survey price, because the weekly survey prices ordinary on-highway ultra-low-sulfur diesel, the grade most trucks pull.

Why the winter blend costs more

Number 1 diesel and kerosene cost more than number 2 at wholesale, and they carry about 2 percent less energy per gallon by EIA's heat-content figures, so a winter blend is both pricier at the rack and slightly worse on fuel economy. Additives are a cost too. The switch runs roughly October through March by region, the same months winter heating demand competes for the same distillate barrel. Diesel gel temperature works through what a typical number 1 cut adds per gallon.

Worked example: the season in the regional numbers

On the live charts above, New England (PADD 1A) and the Midwest (PADD 2) are drawn against the US average across the year. Both burn winter-grade fuel through the cold months, but the season moves their gaps to the national number differently. Each figure below is the region's price minus the US average from the same Monday survey, averaged over the surveys since EIA's June 2022 redesign.

In New England, the gap has averaged +43.0 cents a gallon in December through February and +27.3 cents in June through August, so on average New England diesel has sat 15.7 cents higher against the US average in winter than in summer. In the Midwest, the gap has averaged -9.2 cents a gallon in December through February and -5.0 cents in June through August, so on average Midwest diesel has sat 4.1 cents lower against the US average in winter than in summer.

New England's winter is also its heating-oil season, and New England burns more heating oil than any other region, from the same distillate barrel. Reading a full winter on both charts shows what the season does to each region's price; Diesel gel temperature separates out what the blend itself costs.

Monday Diesel reports the regional pump prices and explains the seasonal mechanics behind them. It does not recommend a fuel, an additive or a blend, and it does not tell a reader when to buy.

Monday Diesel is a free weekly read of the DOE diesel number and what it does per mile. Built entirely from EIA's public data, in your inbox before dispatch, one email a week.