What Temp Does Diesel Gel?
Untreated #2 diesel clouds around 14 F and plugs filters near 10 F. Enter your overnight low and tank size for a risk verdict plus the kerosene gallons or additive ounces to prevent it.
A gelled fuel system is a no-start at the coldest moment of the year. For a bulk tank, the whole-tank kerosene math above is the number no additive bottle label computes: a 10,000 gallon UST needing a 20% blend takes 2,000 gallons of kerosene, a supplier order, not a jug from the parts store.
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Diesel cloud point explained: cloud point vs CFPP vs gel point
Search results scatter diesel's "gel temperature" anywhere from 0 F to 32 F because three different thresholds get mixed together. They are distinct events, they happen in order as fuel cools, and each one has a different consequence.
| Threshold | Untreated #2 diesel | What happens | What you notice |
|---|---|---|---|
| Cloud point | ~14 F | Paraffin wax crystals first appear and the fuel turns hazy | Nothing yet, but the clock is running |
| CFPP (cold filter plugging point) | ~10 F | Wax accumulates on the fuel filter faster than fuel can pass | Hard starts, power loss, stalling under load |
| Gel point | Sustained cold below CFPP | Enough wax forms that the fuel thickens and stops pouring | No start, no fuel movement at all |
The numbers above are representative for untreated #2. Real thresholds move with the regional seasonal blend, biodiesel content, and the specific batch, which is why the calculator applies a 5 F safety margin instead of cutting it to the degree.
What temp does diesel gel, by fuel type
The single biggest variable is which diesel is actually in your tank. Winterized fuel from a cold-region supplier is a different product from the summer #2 sitting in a farm tank since August, and B20 gels warmer than either.
| Fuel | Cloud point | CFPP | Notes |
|---|---|---|---|
| #2 diesel (untreated) | ~14 F | ~10 F | Standard on-road summer diesel |
| Winter blend | ~0 F | ~-10 F | What suppliers deliver in cold months; varies by region |
| #1 diesel | ~-25 F | ~-40 F | Kerosene-type cut; lower energy content per gallon |
| B20 biodiesel | ~20 F | ~15 F | Biodiesel gels warmer; B20 needs earlier treatment than #2 |
| Off-road / dyed diesel | ~14 F | ~10 F | Same chemistry as #2; the dye changes nothing about gelling |
Kerosene in diesel: mixing rules and blend chart
Kerosene (or #1 diesel, the same cut for this purpose) is the traditional bulk fix: each 10 percent of kerosene in the blend improves CFPP by roughly 5 F. The chart below applies that rule to untreated #2. Blend for the coldest forecast night, not the average, and stop at 50 percent; past that point you should simply be buying #1 or asking your supplier for a winterized delivery.
| Kerosene blend | Protected CFPP (from #2 base) | Kerosene per 100 gal of blend | Kerosene per 1,000 gal of blend |
|---|---|---|---|
| 0% | 10 F | 0 gal | 0 gal |
| 10% | 5 F | 10 gal | 100 gal |
| 20% | 0 F | 20 gal | 200 gal |
| 30% | -5 F | 30 gal | 300 gal |
| 40% | -10 F | 40 gal | 400 gal |
| 50% | -15 F | 50 gal | 500 gal |
Add kerosene before or during a fill so it actually mixes; kerosene poured on top of cold, already-clouded diesel stratifies and protects nothing. Blending also slightly lowers energy content and lubricity, which is the price of the protection.
How to keep diesel from gelling
Buy winter fuel where winter happens. In cold months, terminals in cold regions winterize road diesel automatically. Fuel purchased locally and recently is usually already protected; fuel hauled in from warmer regions or bought before the seasonal switch is not.
Treat storage tanks before the cold arrives, not after. Additives and kerosene both need to mix into fuel that is still above its cloud point. For a transfer tank in a pickup, dose at each fill-up. For a bulk tank or UST, treat when the tank is filled in the fall and again with each winter delivery.
Keep water out. Ice plugs filters at 32 F, well before any wax problem, and the symptoms look identical. Draining water separators and keeping tanks full to limit condensation is winter prep as much as any additive. Regular tank cleaning deals with the sludge and water bottom that make cold starts worse.
Match the fuel to the duty. Equipment that must start unattended at -20 F (generators, remote pumps) is a case for straight #1 diesel or a 50/50 blend through the coldest months, accepting the energy penalty for the reliability.
When to use anti gel in diesel
Dose anti-gel when the overnight forecast drops within about 10 F of your fuel's cloud point, when you are running summer-purchased fuel into a cold snap, and any time equipment will sit outside unrun for days in the cold. At the standard 1:1000 label rate, a typical flow improver claims roughly 15 F of CFPP improvement, and severe-cold rates around 1:500 claim 20 F or more. The calculator above converts those generic rates into ounces for your exact tank size. Two cautions: additives are preventive only, and doubling the dose does not double the protection; past the severe rate the label curve flattens.
How to fix gelled diesel (emergency)
If the engine died or will not start and the filter shows cloudy, waxy fuel, the fix is heat first, chemistry second.
1. Get heat into the fuel system. Move the vehicle into a heated bay or garage if at all possible; a few hours above 40 F redissolves the wax on its own. Block heaters, radiant heaters aimed at the tank and lines (never open flame), and even wrapping the filter housing all work at the margin.
2. Use an emergency re-liquifier, not a preventive additive. Products sold as 911-type re-liquifiers are formulated to dissolve wax that has already formed. Pour into the tank and directly into the filter housing per the label. A standard anti-gel poured into a gelled tank does nothing.
3. Replace the fuel filter. The filter is where the wax collected. Once the system will move fuel, a fresh filter (carry spares in winter) prevents an immediate repeat stall, and cracking the new filter full of treated fuel speeds the restart.
4. Then protect the remaining fuel. Once running, treat the tank for the actual forecast using the calculator above, because the fuel that gelled once will gel again tonight.
Winter diesel fuel: what suppliers blend
Terminal winterization is why most drivers never see gelled fuel. From roughly October through March in cold regions, suppliers either blend #1 into #2 (commonly 10 to 30 percent, up to 50/50 in the harshest markets) or dose cold-flow improver at the rack. They shift the blend month by month with the climate. That protection travels with the fuel, so the risk cases are the gaps: fuel bought outside the region, fuel bought before the seasonal switch, and above all fuel stored on site since warmer months. A bulk tank filled in September holds September fuel no matter what the calendar says, which is why the whole-tank blend math above exists. If you operate storage tanks, your supplier can tell you the cloud point of what they delivered; that number replaces the defaults here.
Frequently Asked Questions
What temperature does diesel freeze?
Diesel does not freeze solid the way water does. It gels. Paraffin wax dissolved in the fuel crystallizes as it cools, first clouding the fuel at around 14 F for untreated #2. Filters plug a few degrees below that, and sustained exposure thickens the fuel to an unpumpable gel. True solidification is far below any temperature a treated fuel system should ever see. The practical freezing point to plan around is the cloud point, because wax that has already formed does not fully redissolve until the fuel warms well above it.
What is the best diesel anti-gel additive?
Judge any anti-gel by three things on its label rather than the brand name. First, the CFPP improvement it claims in degrees (15 to 20 F at the standard rate is typical). Second, the treat rate (1:1000 is a standard dose, 1:500 a severe-cold dose). Third, whether it is a preventive flow improver or an emergency re-liquifier. Preventive additives only work when mixed into fuel that is still above its cloud point; no pour-in product un-gels a tank that has already waxed up without warming it first. Buy by the label math, dose for the coldest night in the forecast, and add it at fill-up so it mixes.
What ratio of kerosene do you mix with diesel?
The working rule of thumb is that every 10 percent kerosene in the blend lowers the cold filter plugging point by about 5 F. A 70/30 diesel-kerosene mix therefore buys roughly 15 F of protection over straight #2. Blends beyond 50 percent stop making sense; at that point buy #1 diesel, which is essentially the same cut. Kerosene blending trades some energy content and lubricity for cold flow, so blend for the forecast rather than defaulting to heavy ratios all winter.
Does diesel anti-gel expire?
Most cold-flow improvers keep for several years in a sealed container stored away from temperature extremes, but two failure modes matter. An opened bottle can absorb moisture, and water is exactly what you do not want to add to a winter fuel system. And an additive left in a freezing truck cab can stratify or thicken to the point that it will not pour or mix. Check the label's shelf-life statement, keep the bottle sealed and indoors, and shake before dosing.
Do gas stations sell winter diesel?
In cold regions, yes. Suppliers seasonally winterize road diesel from roughly October through March by blending #1 into #2 or additizing at the terminal, which is why a truck filled from a busy station in Minnesota in January usually runs fine untreated. The catch is timing and geography: fuel bought in a warm region and driven north, fuel bought early in the season before the winter blend switch, and fuel sitting in storage tanks since summer all carry summer-spec cold flow. That last case is the classic bulk-tank problem this calculator's whole-tank kerosene math is for.
Additive doses shown are generic label-rate estimates; always verify against the specific product label before dosing. Cloud point and CFPP thresholds vary by regional seasonal blend, batch, and biodiesel content, and this tool is not a substitute for winterized fuel from your supplier. For fuel feeding critical equipment, get the delivered fuel's actual cold-flow specs from the supplier.
Cloud point, CFPP, and gel thresholds plus the 10% kerosene per 5 F blend rule were compiled by USTContractors.com from ASTM D975 and D6371 specifications and supplier winterization practice. Last verified July 2026.
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