When temperatures drop and frost begins to creep across windshields, even the fluids your diesel engine relies on can be affected by the cold. Diesel Exhaust Fluid (DEF) is no exception.
DEF is a mixture of urea and deionized water, playing a crucial role in reducing emissions in modern diesel vehicles. This fluid typically freezes at around 12°F (-11°C).
So, how do you tell when your DEF has frozen?
Also, how can you prevent this from happening?
Let’s dive in and answer all your burning questions.
This Article Contains:
- At What Temperature Does DEF Freeze?
- What Are the Warning Signs Your DEF Has Frozen?
- Is It Safe to Drive Your Vehicle When the DEF Has Frozen?
- Does DEF Quality Change After Freezing?
- 4 Proven Tips to Prevent Your DEF From Freezing
- Can Using Additives Prevent the DEF From Freezing?
At What Temperature Does DEF Freeze?
DEF typically freezes when temperatures drop to around 12°F (-11°C). It’s made of 32.5% urea and 67.5% deionized water, giving it a much lower freezing point than pure water.
While frozen DEF remains chemically stable, it cannot be pumped or injected until thawed. Fortunately, most diesel vehicles are equipped with DEF heaters that thaw out the frozen fluid when you start the engine.
Keen to learn more?
Check out our detailed guide covering everything you need to know about DEF.
Now, if this fluid has thickened, your vehicle will usually alert you.
What Are the Warning Signs Your DEF Has Frozen?
You’re likely dealing with frozen DEF if you notice any of these symptoms:
- Persistent low DEF light: When the fluid has frozen, the low DEF warning light on your dashboard may remain illuminated, even if the tank is full. This occurs because the system detects that the fluid is unavailable for injection into the exhaust stream.
- Delayed engine starting in cold conditions: In extremely cold weather, a frozen DEF tank may cause the engine to take longer than usual to start.
- Reduced engine performance: Some vehicles may enter a reduced-power mode (sometimes referred to as the “derate” mode) when the DEF system cannot operate. This limits engine output to protect both the engine and the SCR (Selective Catalytic Reduction) system until normal DEF dosing resumes.
Now, you’re probably wondering:
Is It Safe to Drive Your Vehicle When the DEF Has Frozen?
In most cases, it should be safe to drive when the DEF is frozen. That’s because diesel engines are usually designed with heating elements to thaw the fluid when it solidifies.
However, if DEF remains frozen for too long and your vehicle enters a “reduced-power” mode, this can be dangerous when trying to overtake or respond to sudden traffic conditions.
If you suspect your vehicle isn’t thawing out frozen DEF properly, have the system inspected by a qualified mechanic as soon as possible.
Next, let’s check how freezing impacts the effectiveness of your DEF.
Does DEF Quality Change After Freezing?
No, the chemical composition of DEF doesn’t change when the fluid freezes.
Since DEF is a mixture of urea and deionized water, freezing turns the water component into ice. Once it thaws out, it returns to its normal liquid state with the same chemical properties.
But to avoid any performance issues, always ensure your DEF isn’t exposed to cold weather conditions.
4 Proven Tips to Prevent Your DEF From Freezing
Here’s what you need to do to keep the fluid flowing smoothly:
- Store DEF in a temperature-controlled area: To reduce the risk of freezing, store your unused DEF indoors or in a heated storage area whenever possible.
- Park in sheltered or heated locations: Park your vehicle in a garage or other heated spaces during cold months. If that’s not an option, consider covering your vehicle with an insulated blanket to prevent freezing.
- Ensure your DEF heater is in good condition: Most modern diesel vehicles are equipped with DEF tank heaters and heated lines. Always ensure these heaters are in good condition, as they help thaw frozen fluid quickly and keep the DEF system operational.
- Use DEF before its expiration date: To ensure your DEF remains chemically effective, always use it within its recommended shelf life.
Can Using Additives Prevent the DEF From Freezing?
No, mixing DEF with additives is not recommended. Doing this can alter the DEF’s chemical composition, potentially damaging the SCR system or clogging the injectors.
Remember, freezing doesn’t degrade the quality of your DEF. So, you should always opt for thawing out the fluid.
Keep Your DEF System Winter-Ready with AutoNation Mobile Service
When DEF freezes, the SCR system may malfunction, potentially affecting engine performance and the vehicle’s emissions control system. If you notice the warning signs, act immediately to ensure your vehicle stays reliable in cold weather.
With AutoNation Mobile Service, you don’t have to worry about visiting a shop to address DEF-related issues. Our trained technicians inspect your DEF system and resolve the issue right from your driveway.
For your peace of mind, we back our services with a 12-month, 12,000-mile warranty.
Book an appointment today and keep your DEF flowing smoothly, no matter how low the temperature drops.