How Much DEF Does a Truck Use?

Diesel Exhaust Fluid (DEF) is a urea-based solution that reduces nitrogen oxide (NOx) emissions from diesel engines when used with a Selective Catalytic Reduction (SCR) system. As more truck drivers look for ways to save money on rising diesel fuel costs, switching to DEF can be a cost-effective alternative. However, it’s essential to understand how DEF works and how to use and maintain it properly. Here are some key things to keep in mind:


Consider the Cost of DEF

While DEF can help you save money on diesel fuel costs, it’s a consumable product that requires regular purchase and budgeting. A gallon of DEF costs about $0.60 or $0.15 per liter. A typical heavy-duty truck with a 100-gallon (378 liters) DEF tank can expect to spend about $60 on DEF each time the tank is filled.

How Much DEF Does a Truck Hold?

Most light-duty and medium-duty trucks have DEF tanks that hold between three and five gallons. On the other hand, heavy-duty trucks can contain anywhere from 25 to 80 gallons of DEF. It’s essential to monitor the level of DEF in the tank and only fill it up when necessary to avoid adding extra weight to the vehicle. DEF weighs about 9 pounds per gallon, so a full DEF tank on a truck can weigh anywhere from 27 to 45 pounds.

How Many Miles Will 1 Gallon of DEF Last?

A typical DEF tank on a heavy-duty truck can hold up to 100 gallons (378 liters) of DEF, and most require one gallon of DEF for every 50 gallons of diesel fuel. One gallon of DEF generally lasts between 300 and 500 miles. It’s essential not to let the DEF tank become empty, as this can cause irreversible damage to the DEF pump and system. Always use high-quality DEF that meets American Petroleum Institute (API) standards to avoid clogging the system and reducing efficiency.

How Often Do You Put DEF in a Diesel?

Most DEF tanks must be refilled once every 3 to 4 times you refuel with diesel fuel. Diesel fuel lubricates the engine and keeps it running smoothly, but it also produces harmful emissions. Many diesel engines now have a diesel particulate filter (DPF) that traps soot and other particles to reduce these emissions. Cleaning the DPF requires using DEF, which reacts with the soot particles and breaks them down into harmless gases.

What Happens if You Run Out of DEF?

Running out of DEF can cause a loss of power, reduced efficiency, and, eventually, total engine failure. In addition, the emission control system will no longer function properly, causing black exhaust emissions, which are bad for the environment and against the law in many states. It’s essential to regularly check your DEF level and top it off as necessary to avoid potential damage to your engine and costly repairs.


DEF is essential to a diesel engine’s emission control system. It helps reduce emissions and keeps the engine running smoothly. Regularly checking your DEF level and using high-quality DEF that meets API standards can help prolong your engine’s life and avoid costly repairs. While DEF may require additional budgeting and monitoring, the cost savings on diesel fuel make it a viable alternative for many truck drivers.

About the author, Laurence Perkins

Laurence Perkins is the passionate car enthusiast behind the blog My Auto Machine. With over a decade of experience in the automotive industry, Perkins has knowledge and experience with a wide range of car makes and models. His particular interests lie in performance and modification, and his blog covers these topics in-depth. In addition to his own blog, Perkins is a respected voice in the automotive community and writes for various automotive publications. His insights and opinions on cars are highly sought-after.