Diesel Won't Start in the Cold: What to Check First
Updated: 3 hours ago
It's 5°F in Colorado Springs, the truck cranks slow, and it won't fire. Before you blame the fuel, work through the problem in order. On many diesels, a cold no-start comes down to four things: battery power, the intake heating system, fuel that can't flow, or oil that's too thick for the starter to spin through.
We work on Ford Power Stroke, GM Duramax, Ram Cummins and Isuzu NPR trucks every winter at Westco. This is the same order our ASE-certified techs think through when one gets towed in on a January morning.
Is it the fuel, or is it something else?
Often it's something else. Gelled fuel gets the blame, but weak batteries and failed glow plugs cause plenty of cold-morning no-starts too, and they're quicker to rule out. Work down this list before you reach for a bottle of anything.
1. Batteries and cables
A diesel needs a lot of cranking speed to build the heat that lights the fuel. Many diesel pickups carry two batteries, and one weak battery can drag the pair down. Cold weather also cuts how much power a battery can deliver.
Signs it's the batteries: slow, labored cranking, clicking, or dash lights that dim hard while cranking. Corroded or loose cables do the same thing. If it cranks fast and strong but won't fire, move on.
2. Glow plugs or the grid heater
A diesel has no spark plugs. It lights fuel with the heat of compressed air, and on a cold engine that isn't enough on its own. Power Stroke and Duramax engines use glow plugs to preheat the cylinders. Many Ram Cummins trucks use an intake grid heater that warms the incoming air instead, and the newest Ram heavy-duty trucks have moved to glow plugs.
Signs it's the heating system: the "wait to start" light behaves oddly, the engine cranks at normal speed but won't catch, or it starts rough with a cloud of white smoke and clears up once it warms. One or two dead glow plugs often show up as a rough, smoky start before they turn into a no-start.
On a 7.3 Power Stroke, the glow plug relay is a common culprit; see how we bulletproof a 7.3. On a 6.0, a rough, smoky cold start that smooths out as it warms often points to sticky injectors; see what fails on a 6.0 Power Stroke.
3. Gelled fuel filter or ice in the water separator
These two look alike, but they're different problems.
Gelled fuel: wax in the diesel comes out of solution and plugs the fuel filter. The truck may start, run a minute, then stall, or it may crank and never fire.
Ice: diesel picks up water from condensation and from storage tanks. The water separator collects it. If it isn't drained, that water can freeze at 32°F and block flow, even on a day that's nowhere near cold enough to gel the fuel.
If your truck has a water-in-fuel light, don't ignore it heading into winter.
4. Oil thickness
Cold oil is thick oil. If the engine has the wrong viscosity for the season, or the oil is overdue, the starter has to fight harder and cranking speed drops. That feeds straight back into problem one. Your owner's manual lists the viscosity grades approved for cold temperatures.
What temperature does diesel gel at?
There's no single number. It depends on the fuel. Regular No. 2 diesel commonly starts clouding somewhere between the teens and about 20°F, and some batches cloud lower. Winter-treated or blended fuel can go much lower.
It helps to know three terms:
Cloud point: the temperature where wax crystals first form and the fuel looks hazy. A university extension resource puts No. 2 diesel's cloud point anywhere from about −18°F to +20°F, and No. 1 diesel's near −40°F. A fuel cooperative's guidance uses about 14°F as a typical No. 2 cloud point.
Cold filter plugging point (CFPP): the temperature where those crystals start plugging a filter. It sits at or below the cloud point, and additives are designed to push it lower.
Pour point / gel point: where the fuel barely moves at all. By then your filter has long since plugged.
Fuel still flows at its cloud point, but that's where trouble starts. The national diesel fuel standard, ASTM D975, doesn't set one cold-weather number for everyone. Instead, low-temperature performance is agreed between the fuel supplier and buyer for the season and region. That's why diesel from one station, or one week, can behave differently from the next.
Can anti-gel additive fix a truck that's already gelled?
No. Anti-gel (cold flow) additives work by changing how wax crystals form as the fuel cools, which keeps them small enough to pass through the filter. They have to be in the fuel before it reaches its cloud point. Once crystals have formed, a fuel supplier's own guidance says they stay put, even if you blend the fuel afterward.
If your truck has already gelled, that's a different situation:
Get the truck somewhere warm, or warm the fuel filter and lines.
Products sold as emergency treatments for gelled fuel are formulated differently from everyday anti-gel. Follow the label exactly.
Plan on replacing the fuel filter. A filter full of wax often stays restricted even after the fuel warms up.
Prevention is far easier: treat the tank before a cold snap, not during one.
Should I add gasoline or kerosene?
No. It's old advice, and it doesn't fit modern diesels.
Gasoline: Today's high-pressure common-rail fuel systems depend on diesel fuel to lubricate the injection pump. Gasoline has almost none of that lubricity. Vehicle makers with common-rail engines prohibit diluting diesel with gasoline because it can damage the injection system. Gasoline also makes the fuel in your tank far more flammable. One truck maker's fuel bulletin warns plainly not to mix gasoline with diesel because of the risk of explosion.
Kerosene from a hardware store or heating-oil supplier: It isn't made to the on-road diesel standard. It may not have the lubricity your injection pump needs, and it may not meet the ultra-low sulfur level your exhaust aftertreatment system was built for.
What people are really after with "add kerosene" is No. 1 diesel. That's a lighter on-road diesel fuel that fuel suppliers blend with No. 2 at the terminal to lower the cloud point. Industry guidance from Daimler Truck North America calls blending with No. 1 the most effective way to lower cloud point. That blending belongs at the fuel terminal, not in your driveway.
Do Colorado Springs stations sell winter-blend diesel?
Winter-treated diesel is common in Colorado, but what's in any one pump varies, so don't assume. Winter diesel in Colorado is commonly regular diesel treated with cold-flow additives, sometimes blended with No. 1. One fuel distributor serving the Rocky Mountain region says it starts adding winter additives around October 15 and stops around March 15. The same distributor says Denver mostly gets standard diesel with additives, while the Western Slope gets a No. 1 / No. 2 blend.
What's actually in a given Colorado Springs pump depends on the station, its supplier, and when its tank was last filled. Some practical steps:
Ask the station if its diesel is winter-treated, and to what temperature.
Fill up at busy truck stops. Their tanks turn over fast, so fall fuel is less likely to be sitting there in January.
If a hard cold snap is on the way, treat your tank with an anti-gel additive before it hits.
If you're heading up Ute Pass or into the mountains, remember it's colder up there than it is in town.
When should I tow it in?
If the truck cranks strong but won't fire after you've ruled out the battery, or if it keeps stalling after a warm-up, it's time. Repeated cranking on a diesel that won't catch can drain the batteries and overheat the starter.
When a cold-weather no-start comes to Westco, our techs typically:
Load-test the batteries and check the cables and connections.
Test the glow plugs or grid heater and their control circuit.
Service the fuel filters and water separator, and look at what comes out. Wax, water and debris each point to different fixes.
Check the block heater, if your truck has one. A block heater that's quit working often gets discovered on the first cold morning.
Scan for fault codes that point to fuel pressure, sensors or the heating system.
Better yet, bring it in for a free inspection before the first freeze, so these get checked before they leave you stuck.
Learn more on our diesel service page, or see our pages for Ford Power Stroke, GM Duramax and Ram Cummins.
FAQ
Should I plug in my block heater every night?
On cold nights, a block heater makes starting much easier on the engine and batteries. Many owners plug in when the forecast drops into the teens or below. Your owner's manual may give a specific temperature.
Does idling a diesel all night keep the fuel from gelling?
It can keep fuel moving, but long idling has its own costs on modern diesels, including soot buildup in the exhaust filter. A block heater, treated fuel and a healthy battery are usually a better plan.
Can I just replace the fuel filter myself when it gels?
Some owners do. On many modern trucks, though, the fuel system has to be primed correctly afterward, and air in the system can cause its own no-start. If you're not sure, bring it in.
Bring it to Westco
Westco Automotive & Truck Repair is a female-led shop that's been fixing diesels in Colorado Springs since 2018. Our techs are ASE-certified, we're CARFAX Top Rated and RepairPal Certified, and our repairs carry a 24-month / 24,000-mile parts and labor warranty. We also do not do emissions deletes. We fix the truck the way it was built to run.
Related Westco services
Get ahead of the first cold snap. Book my FREE Inspection or call (719) 591-7743. We're at 1130 Valley St, Ste A/B, Colorado Springs, open Monday–Friday, 9–5.
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