Can a Diesel Truck Run Without DEF Fluid?


Can a Diesel Truck Run Without DEF Fluid?

Diesel Exhaust Fluid, or DEF, reduces the amount of harmful chemicals that are emitted by your vehicle. In 2010 the Environmental Protection Agency (EPA) has established new guidelines that require diesel vehicle manufacturers to make it harder for the vehicle to start if the diesel exhaust fluid runs out so that the owner of the vehicle takes the issue seriously.

Can a Diesel Truck Run Without DEF Fluid?

In some trucks with low levels of DEF fluid or without any DEF fluid, the trucks ran sluggish and would not go faster 5 mph. The truck’s power output drastically reduces, and if the vehicle runs out of fluid, it will not start, or its speed will not exceed 5 mph. A red warning light is displayed on the dashboard screen until the fluid is replaced.

Manufacturers are also required to provide a system on the dashboard display that will alert the driver when the Diesel Exhaust Fluid tank level drops below 10%.

When the DEF level in the tank goes below ten percent, an amber warning light will come on the dashboard display. When it falls below 5%, this light starts to flash, and when it drops below 2.5%, the lights become brighter.

What Is DEF?

The Diesel Exhaust Fluid (DEF) is a non-toxic solution that features 32.5% of Urea mixed with 67.5% of de-ionized water. Its primary function is the reduction of harmful NOx emission gases in diesel-powered vehicles, which are present in the exhaust gases, into nitrogen and water that are harmless to the environment.

How Much DEF Will My Truck Consume?

The amount of DEF consumed varies from one truck to another. The diesel exhaust fluid consumption is always measured as a ratio of your vehicle’s mpg.

This ratio is also referred to as a dosing rate or treating rate. The treat rate of medium and heavy-duty trucks is normally between 2 to 3 percent.

For example, if your vehicle has a fuel economy of 8 mpg and a treat rate of 2%, your vehicle will use 1 gallon of diesel exhaust fluid every 400 miles. The treat rate is normally lower than most manufacturers’ specifications.

How Does Diesel Exhaust Fluid Work?

When the exhaust gases leave the combustion chamber, they contain harmful gases such as nitrogen oxides, carbon monoxide, Sulphur dioxide, and soot. The exhaust gases pass through a particulate filter, which removes any soot or ash that may be present.

After the particulate filter, the exhaust gases flow past a nozzle that continuously sprays diesel exhaust fluid. This fluid consists of de-ionized water and pure Urea.

The mixture of the diesel exhaust fluid and hot exhaust gases are directed through the catalytic converter. Here, the diesel exhaust fluid and the hot exhaust gases, in the presence of catalysts and several metal compounds, reduce nitrogen dioxides and monoxides to harmless and environmentally friendly nitrogen and water. 

Most cars combine this system, known as Selective Catalytic Reduction (SCR), with an exhaust gas recirculation system. This system returns part of the exhaust gases into the combustion chamber to complete the combustion of unburnt gases.

Does The Diesel Exhaust Fluid Freez The Tank?

During cold weather, there is always a possibility of the diesel exhaust fluid freezing. The Diesel Exhaust Fluid freezes at 120 F (-110 C) and vaporizes at temperatures above 860 F.

Many trucks are equipped with in-tank heating elements or other methods to de-freeze the fluid tank. The DEF feeder and supply tubes are also heated to prevent them from freezing, and they are emptied when the engine stops.

This process is done to prevent the tubes from freezing. You should not worry about your diesel exhaust fluid freezing because most vehicle manufactures have sorted this problem out.

What Will Happen If The Diesel Exhaust Fluid Tank Is filled With Diesel?

If your vehicle smells like gas, it’s likely unrelated to the DEF. It is very hard to confuse diesel exhaust fluid tubes and diesel filler necks. There are standard nozzle diameters for the exhaust fluid and diesel. The DEF nozzle measures 0.75 inches, while the Diesel Nozzle measures 0.87 inches standard.

The Diesel Exhaust Fluid filling cap is marked blue and is always marked ‘Diesel Exhaust Fluid.’ However, if you accidentally fill the DEF tank with diesel, it will float on top of the Diesel Exhaust Fluid, and your engine will not start. If this happens, take your vehicle to the service center for repair.

Diesel Exhaust Fluid Shelf Life: How Long Is It?

When stored in a cool place, the Diesel Exhaust Fluid can last up to two years. But if not stored well, unprotected from direct sunlight or if stored in an area where temperatures are above 860F, the shelf life of the fluid will drastically reduce. The Diesel Exhaust fluid should contain an expiry date on its packaging.

Is Diesel Exhaust Fluid Corrosive Or Toxic?

Diesel Exhaust Fluid is non-toxic. It is the least non-toxic fluid used in vehicles apart from water. The exhaust fluid is corrosive to some metals, including carbon steel, copper, aluminum, and zinc.

Will DEF Lower My Fuel Mileage?

DEF fluid does not low the fuel economy of your vehicle. Studies have shown that vehicles with Selective Catalytic Reduction have a better fuel economy than those with other systems.

However, many manufacturers have designed their automobiles to produce less power when the diesel exhaust fluid level is below 2.5%. This reduces the fuel economy of the car.

Can I Add An Anti-Freezing Solution To The DEF Mixture To Keep It From Freezing?

No additive should be added to the diesel emission fluid to prevent freezing. Additives would contaminate the DEF and prevent it from performing its function. Vehicles have already been equipped with technologies that prevent freezing of the emission fluid.

How Often Do You Need To Fill Up The DEF Tank?

Two things determine how often you should fill up your diesel exhaust fluid tank.

  1. The size of your DEF tank and
  2. Your truck’s fuel economy.

An average medium-duty truck will use 2 to three gallons of DEF per 10,000 miles. Some trucks are equipped with a gauge readout of exactly how much diesel emission fluid is available in the tank.

Selective Catalytic Reduction: What Is It? How Does It Affect Your Vehicle?

The SCR is an emission control system that uses chemical reduction processes to convert harmful gases to non-toxic environment-friendly gases. It uses Diesel Exhaust Fluid to reduce nitrogen dioxide and nitrogen monoxide to nitrogen and water.

This process is enhanced by metal catalysts. It reduces the emission of harmful gases by 90% and reduces fuel consumption by 4%. SCR also increases the power output of the vehicle.

Does The EPA Require All Diesel Vehicles To Be Fitted With SCR?

The EPA required all diesel vehicles manufactured after 2010 to be fitted with an SCR (Selective Catalytic Reduction) system to reduce the emission of harmful gases. Intending to achieve zero-emission, the EPA is becoming stricter on the allowable percentage of emission gases. The EPA launched the ” Cleaner Truck Initiative,” which is aimed at improving the SCR systems so that emission is reduced to zero. 

What Should I Do If I Spill DEF?

Sand is normally used to absorb spilled DEF fluid. You can also use a lot of water to rinse and clean the area contaminated by the DEF.

Keep in mind that DEF is non-toxic and is only mildly caustic. A DEF spill is no need for an emergency.

SCR Systems

SCR is becoming one of the most important parts of diesel vehicles. With emission rules and regulations becoming stricter, diesel truck owners should ensure their automobile’s SCR systems are in good condition.

Also, it is essential to ensure the diesel exhaust fluid level is sufficient. Modern trucks will not run without the DEF. Hence the need for diesel truck owners to check their fluid levels frequently. Reducing emissions should be everyone’s goal. Maintaining your vehicle would also reduce emissions and DEF consumption.

Kern Campbell

I've had a passion for four-wheel-drive vehicles since I was a kid riding in the back seat of my Grandfather's Jeep Grand Wagoneer. I have owned a lot of vehicles over the years. They each have their pros and cons and I look forward to sharing my knowledge with you so you can find the vehicle that's just right for your needs.

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