Understanding DEF Regulations: How Much DEF Do Trucks Need?

Diesel exhaust fluid (DEF) is a critical component in reducing harmful emissions from heavy-duty vehicles to comply with environmental protection laws. These regulations differ by state and between the state and federal levels, cementing the importance of understanding your vehicle’s DEF use and capacity to comply.

Table of Contents

• What Requirements Apply to DEF?
• How Much DEF Does a Truck Hold?
• How Much DEF Does a Truck Use?
• How to Monitor DEF Levels
• Partner With Foster Fuels for Your DEF Needs

What Requirements Apply to DEF?

The U.S. Environmental Protection Agency is the driver of DEF regulations at the federal level. These primarily apply to newer models of heavy-duty vehicles and trucks that can be retrofitted. Exemptions can apply to vehicles with lighter Gross Vehicle Weight Rating (GVWR) and those with older engines incapable of using a selective catalytic reduction (SCR) necessary to negate nitrogen oxides (NOx).

Many states have also enacted laws governing DEF use on their public highways. For example, Pennsylvania statutes apply to most vehicles with a GVWR of 14,000 pounds or higher and must follow the rules established by the California Air Resources Board.

How Much DEF Does a Truck Hold?

DEF capacity varies widely between vehicle manufacturers and models and often correlates to fuel tank size. In other words, the larger your fuel tank, the higher your truck’s DEF capacity. Your owner’s manual is the best source of information for your specific truck and its DEF tank size.

How Much DEF Does a Truck Use?

Most industry professionals measure DEF consumption as a percentage of their overall fuel use. An average of 2% to 3% is common, but the SCR system injects DEF as needed to offset emissions’ harmfulness. As a result, many factors can impact DEF consumption rate:

• Operating environment: Vehicles that often encounter stop-and-go traffic and hills will use more DEF. The engine works harder to compensate for these conditions, generating more NOx.
• Driving patterns: Drivers who operate at higher speeds or engage in more aggressive driving behavior will increase DEF consumption in their vehicles.
• Engine metrics: The higher the engine horsepower and the bigger its size, the more NOx it produces and the more DEF it needs to negate that.
• Load weight: Heavier loads also force the engine to work harder, which results in more DEF use.

How to Monitor DEF Levels

Monitoring your DEF level is vital for compliance and protecting expensive SCR systems from damage. Fortunately, doing so is pretty straightforward in most modern diesel vehicles — your dashboard should have a DEF indicator similar to your fuel tank gauge. Best practices include refilling DEF when the indicator signals about 25% remaining.

Partner With Foster Fuels for Your DEF Needs

Foster Fuels has been helping businesses manage fuel operations for over 100 years. We’re a strategic partner for diesel exhaust fluid delivery in all 48 contiguous states and a federal government prime contractor. Trust us to help support your fleet’s legal compliance, keep your vehicles on the road and prevent costly downtime. Contact our DEF experts to discuss how we can help.