DEF Frequently Asked Questions

Does it cost more to operate a 2011 Super Duty since it requires DEF?

A primary advantage of having SCR/DEF on the new Power Stroke diesel engine is the 5-8 percent increase in fuel efficiency compared to a diesel engine using a Lean NOx Trap. This means the 2011 Super Duty is more efficient to operate than a Ram Pickup and the 2010 Super Duty models. Here’s a quick look at the potential annual SCR/DEF operating costs/savings:


  • DEF is $3-5 per gallon
  • Customer will use approximately 5 gallons every 7500 miles
  • Customer will see a 5-8 percent improvement in fuel efficiency compared to an LNT system

Operating Costs/Savings

  • Two DEF refills = $30-50
  • Fuel savings = $142-222 ($3 per gallon)
  • Total annual savings is $92-192

BOTTOM LINE: 2011 Super Duty is more cost effective to operate than Silverado HD even with both vehicles using an SCR/DEF system.

When should the DEF tank be refilled?

Customer will receive a number of audible warnings and dash messages, beginning at approximately 800 miles before the DEF tank is empty. Under normal operation, the DEF should only require filling with the recommended oil change intervals. Towing can increase DEF consumption.

Will the truck still run if refill warnings are ignored?

The truck will experience reduced engine speeds as the DEF tank approaches empty, eventually forcing the engine idle when the DEF tank is depleted.

If a truck is not used for a while, will the DEF need to be replaced?

The system will monitor DEF quality and adjust for conditions of use or non-use. The warnings and dash messages will indicate when the fluid needs to be refilled.

Can new DEF be added to the DEF already in the tank?

Yes. Motorcraft DEF is widely available in 1 and 2.5 gallon bottles for customer use. Ford recommends only API-certified DEF.

Will DEF freeze?

DEF has a freezing point of 12 degrees Fahrenheit (F). The DEF tank, supply module and lines are heated to help prevent freezing while the truck is in operation as well as thaw any frozen fluid once started. DEF expands when it freezes; the DEF tank is designed to allow for this expansion.

Can the truck be started and operated if the DEF is frozen?

Yes, the truck can be started and operated while the DEF thaws.

Where is the DEF fill port located?

It is located on the driver’s side of the truck next to the diesel fuel filler and is easily identified by its smaller, blue cap.

What if the wrong fluid is added to the DEF tank?

If improper fluid is added, the DEF tank must be drained completely before adding additional DEF to avoid contamination. The truck should be immediately taken to the dealer for service if improper fluid is added.

What is the shelf life for DEF?

DEF has a minimum shelf life of one year if stored between 12 and 86 degrees F. Note that in warmer climates, DEF will have a shorter shelf life.

Learn More

Watch this short tutorial on how to properly fill your DEF tank and when to fill it according to the message center in the instrument cluster:

DEF is available at Fuller Ford in 1 gallon bottles or in bulk. Call our parts department at (513) 352-5870 or (888) 893-7505 or contact us at http:// for more information.

As always, Fuller Ford offers Lifetime Free Oil Changes on ALL new vehicle purchases – in stock or factory ordered. This includes the entire Super Duty line-up! Fuller Ford is the Cincinnati Tri-State Region’s truck leader. Whether you are coming from Ohio, Kentucky, or Indiana, we are conveniently located right off of I-75, just west of downtown Cincinnati. Fuller Ford can help you with all your Super Duty questions and needs! Check out our entire inventory at


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