Diesel #1 vs #2: What's the Difference?
#1 is the thin, cold-weather grade. #2 is the everyday fuel. The ASTM specs side by side, how winter blends work, and which one belongs in your tanks.
#1 diesel is the lighter, thinner grade. It's close to kerosene, carries less wax, and stays fluid at temperatures that would cloud and plug a filter on #2. The trade-offs: a few percent less energy per gallon, slightly lower natural lubricity, and a higher price.
#2 diesel is the standard year-round fuel. It's what US trucks, equipment and generators burn most of the year. It has more energy per gallon and costs less, but it starts to cloud somewhere around 6–14°F. In cold months, suppliers blend #1 into #2 or treat it with cold-flow additives. That's "winter diesel."
#1 vs #2 diesel: comparison table
Both grades are defined by ASTM D975. On-road and nonroad diesel in the US is the S15 version of each, meaning 15 ppm sulfur maximum. So sulfur is not a difference between them, whatever older articles say. The real differences are volatility, viscosity, cold flow and energy.
| Property | #1 diesel (No. 1-D S15) | #2 diesel (No. 2-D S15) |
|---|---|---|
| What ASTM calls it | "Special-purpose, light middle distillate" for engines that need higher volatility | "General purpose" middle distillate, especially for varying speed and load |
| Viscosity at 40°C | 1.3–2.4 mm²/s | 1.9–4.1 mm²/s |
| 90% distillation point | 550°F (288°C) max | 540–640°F (282–338°C) |
| Flash point, minimum | 100°F (38°C) | 126°F (52°C) |
| Cetane number, minimum | 40 | 40 |
| Cloud point / cold flow | Not fixed by D975. Lower wax content; CHS recommends straight #1 below -30°F | Not fixed by D975. Typically clouds around 6–14°F, depending on the supplier |
| Sulfur | 15 ppm max | 15 ppm max |
| Lubricity (HFRR) | 520 µm max wear scar. Naturally a little lower than #2 | 520 µm max wear scar |
| Carbon residue | 0.15% max | 0.35% max |
| Energy per gallon | A few percent less than #2 | ≈ 128,500 Btu (lower heating value); ≈ 138,500 (higher) |
| Weight per gallon | Usually described as lighter for #1; published figures vary. See diesel weight per gallon. | |
| Typical price | Higher. EIA refiner wholesale: 19–49¢/gal above #2 every year 2010–2020 | Baseline |
| Typical uses | Winter blending stock; straight in severe cold; fuel that sits outside in sub-zero weather | Year-round fuel for trucks, equipment and generators; what most US pumps sell |
Spec limits from ASTM D975-24, Table 1. Cloud point is set by agreement between supplier and buyer for the season and region, not by the spec. #2 energy: DOE Alternative Fuels Data Center (ULSD). #1 energy: Chevron's Diesel Fuels Technical Review says "a few percent lower" because #1 is less dense. Sources disagree on the size of the gap: heating-oil tables put No. 1 at 132,900–137,000 Btu/gal gross vs. 137,000–141,800 for No. 2, while EPA's emissions-reporting defaults rate No. 1 and No. 2 almost the same (139,000 vs. 138,000 Btu/gal). Plan on a few percent, not 10%.
Looking for #4 diesel, ULSD vs. dyed, biodiesel or R99? Those are covered in diesel fuel grades explained. This page sticks to #1 against #2.
What the numbers meanWhat actually changes when you switch from #2 to #1
Less wax, so it stays liquid colder
All diesel contains paraffin wax, and the higher-boiling #2 carries more of it (Cummins). When fuel cools to its cloud point, that wax comes out as crystals and plugs filters. #1 is cut lighter, so it clouds at a much lower temperature. More on what temperature diesel gels.
Fewer Btu in every gallon
Diesel is sold by volume, and #1 is less dense, so each gallon holds a few percent less energy. Chevron puts the fuel-economy loss at about the same few percent. Cummins notes that blended winter fuel costs more for both reasons: a higher price and lower energy content.
Same spec, thinner fuel
Both grades must pass the same 520-micron lubricity limit. Chevron says #1's lubricity is likely a little lower because of its lower viscosity: not enough to cause sudden failure, but a steady diet in equipment designed for #2 may mean more long-term fuel-system wear.
Cetane close, flash point lower
Both grades need a cetane number of at least 40. Chevron says #1 may run one or two numbers below #2. #1's minimum flash point is 100°F against 126°F for #2.
How winter blends of #1 and #2 work
"Winter diesel" isn't a separate ASTM grade. It's #2 made to work in the cold, in one of two ways:
- Dilute it with #1. Blending a low-wax fuel into #2 lowers the cloud point, and it's the only practical way to do that once fuel is in the distribution system (Chevron, Detroit). ASTM D975 calls it "normal blending practice" when a cloud point below 10°F (-12°C) is specified. The blend still counts as #2, with the flash point minimum relaxed to 100°F and the viscosity minimum to 1.7 mm²/s.
- Treat it with cold-flow additives. Flow improvers change the size and shape of wax crystals so fuel keeps passing the filter below its cloud point. They lower the cold filter plugging point (CFPP) and pour point, but do little for the cloud point itself (Detroit). They're cheaper than blending and don't cost fuel economy (Chevron). Many winter fuels use both.
| Expected temperatures | Typical blend (#2 / #1) | Source |
|---|---|---|
| Below about 30°F | 70 / 30 | CHS cold-weather guidance |
| Near 0°F | 30 / 70 | CHS cold-weather guidance |
| Below -30°F | Straight #1 | CHS cold-weather guidance |
| Rule of thumb | Each 10% #1 lowers cloud point ~2–3°F | Chevron, Cenex, CHS: ~3°F. Cummins: 30–60% light distillate gives a 5.4–12.6°F drop |
The ratio sources don't fully agree, so treat ratios as a starting point and judge a winter fuel by its measured cloud point and CFPP. Local suppliers set their blends by region and month.
How to know what winter fuel you're getting
- Ask for numbers, not a ratio. The cloud point and CFPP of the delivered fuel tell you how cold it will run. ASTM D975 leaves cold-flow limits to agreement between supplier and buyer, so ask.
- Match them to your coldest day. Cummins wants the cloud point at least 11°F (6°C) below the lowest temperature the fuel will see. ASTM D975 publishes tenth-percentile minimum temperatures by state for October through March as a planning guide.
- Blend before the cold, not during it. Lighter fuel has to be added before wax forms to work (Cummins). Once a tank has clouded, adding #1 won't clear it until the fuel warms up.
- Check what's already in the tank. A generator or jobsite tank filled in August still holds August fuel in January. Stored tanks need their fuel winterized, not just new deliveries.
- Don't double-dose additives. Cummins says to ask whether the fuel already contains a winter additive, because overuse can plug filters.
Step-by-step prevention for trucks, equipment and tanks is in how to prevent diesel gelling.
Which one#1 or #2 diesel: which should you use?
Use #2
For heavy year-round work (trucks, loaders, excavators, generators that run in mild weather), #2 is the default. More energy per gallon and a lower price mean more work per dollar.
Use a winter blend
Where temperatures drop toward your fuel's cloud point, a #1/#2 blend or additized #2 keeps filters clear without giving up all of #2's economy.
Use straight #1
Sustained sub-zero operation, roughly -30°F and below per CHS, is where straight #1 earns its price. Expect to burn a few percent more fuel.
Standby generators & outdoor equipment
Equipment that sits outside, and standby generators with outdoor tanks, can't warm their fuel first. Get the tank winterized before the first hard freeze; a gelled generator fails the moment you need it.
Can you mix #1 and #2? Yes. Mixing them is exactly what a winter blend is, and ASTM D975 calls it normal practice. The mix behaves somewhere between the two: lower cloud point than #2, less energy than #2.
Can #1 run in any diesel engine? Both grades are made for compression-ignition engines, and Chevron notes #1 is used straight in cold weather. Cummins' fuel spec accepts a viscosity range of 1.3–4.1 mm²/s, which covers both grades. Still, check the owner's manual: OEMs set their own minimums, and Cummins asks for a cetane number of at least 45 below 32°F, higher than the D975 minimum of 40.
KeroseneIs #1 diesel the same as kerosene?
Close, but not the same product. ASTM describes No. 1-D as fuels "from kerosine to the intermediate middle distillates", and Chevron groups kerosene and Jet A with #1 as similar fuels. The difference is what each is certified for:
| #1 diesel (No. 1-D S15) | Kerosene (No. 1-K) | |
|---|---|---|
| Specification | ASTM D975, for diesel engines | ASTM D3699, for heaters, stoves and lamps |
| Sulfur | 15 ppm max | 0.04% (400 ppm) max |
| Cetane & lubricity | Cetane 40 min; lubricity 520 µm max | Not part of the D3699 spec |
| Federal excise tax | Same: 24.4¢/gal for diesel and kerosene. Dyed diesel and dyed kerosene are exempt for qualifying off-road use. | |
Federal rules allow ULSD that also meets kerosene or jet fuel specs ("dual-use kerosene") to be designated as either one. Unless kerosene is certified as 15 ppm diesel, don't put it in an engine with a DPF or SCR system: 400 ppm sulfur is far above what those systems are built for. For heating, see what heating oil is (#2 fuel oil is the heating-oil cousin of #2 diesel).
Dyed vs. clearDyed off-road #1 and #2
Grade and tax status are separate. The federal dye rule applies to diesel fuel and kerosene sold for tax-exempt use, whatever the grade, so dyed fuel can be #2, #1 or a winter blend. What's offered locally depends on the terminal and the supplier. The rules are the same as for any dyed diesel: off-road equipment, generators and farm machinery only, never a licensed road vehicle. See off-road diesel delivery, on-road diesel delivery, and current per-gallon rates in diesel taxes by state.
Topping up a clear on-road tank with dyed #1 to fight gelling puts dyed fuel in a road vehicle. Keep winter fuel dyed or clear to match the equipment.
The right seasonal diesel, delivered to your tanks
FuelGo delivers dyed off-road and clear on-road diesel nationwide: 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. We match the fuel to your engines and how you're taxed, including winter blends, and offer winter blending and additive packages for tanks and equipment that sit outside. Ask dispatch before the first cold snap, not after a filter gels.
If a tank has already clouded or holds old fuel, fuel polishing, tank cleaning and lab fuel testing sort out what's in it. For larger sites, bulk fuel delivery keeps the switch to winter fuel on schedule. Dispatch runs 24/7/365: get a free quote or call 800-720-4546. A dispatcher replies within the hour.
Common questionsDiesel #1 vs #2 FAQ
What is the difference between #1 and #2 diesel?
Is #1 diesel the same as kerosene?
Can you mix #1 and #2 diesel?
Which is better, #1 or #2 diesel?
Why is #1 diesel more expensive?
What is winter diesel?
Does #1 diesel hurt my engine?
Is gas station diesel #1 or #2?
Sources: ASTM D975-24, Standard Specification for Diesel Fuel (NCWM copy) · DieselNet, US diesel fuel standards · 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 · AFDC Fuel Properties Comparison · EPA 40 CFR 98 Table C-1 · Engineering ToolBox, fuel oil heating values · EIA, No. 1 distillate refiner wholesale price · EIA, No. 2 diesel refiner wholesale price · ASTM D3699 kerosene requirements (COMAR 03.03.05.03) · 40 CFR 1090.1015, dual-use kerosene · IRS Publication 510, fuel excise taxes