How Long Does DEF Fluid Last?

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A person refilling their RV with DEF fluid after finding out how long it lasts

Drivers with a modern diesel engine are likely familiar with DEF fluid. Keeping DEF fluid in your vehicle’s DEF tank is essential.

While the fluid is readily available at most big-box retailers, gas stations, and auto part stores, many drivers keep a generous supply on hand, so they never run out. So how long does DEF fluid last?

Today, we’re answering this crucial question and sharing vital information regarding the DEF fluid you put in your vehicle. Start your engines, and let’s dive in!

What Is DEF Fluid?

DEF Fluid is a mixture of chemicals that injects into a diesel vehicle’s exhaust system. The fluid helps reduce the harmful gasses created while running these engines.

It began to become standard on diesel-powered passenger cars and trucks in 2010. Drivers can purchase DEF fluid at the pump at truck stops, by the jug at big-box retail establishments, and at any other location that stocks automotive supplies. 

Benefits of DEF Fluid

There are a handful of benefits to using DEF in passenger and commercial vehicles. Let’s examine why DEF fluid is a good thing for drivers to use with their diesel vehicles.

Less Pollution

Diesel-powered vehicles can create a high amount of harmful emissions. Luckily, the DEF fluid uses Selective Catalytic Reduction (SCR) to clean the Nitric oxide from the exhaust.

The more we learn about the impacts of vehicle exhaust on our environment, the more driven we become to reduce our impact on it.

Using DEF fluid and the Selective Catalytic Reduction process, the exhaust turns into nitrogen and water. This combination is much more environmentally friendly than NOx emissions.

Reduces Maintenance

Manufacturers have honed in on the SCR technologies to maximize their use. Vehicles using these technologies tend to experience less wear and tear.

Avoiding costly breakdowns means you and your car can stay on the road. You didn’t spend all of that money on your vehicle for it to sit in a repair shop.

A close up of a def fluid cap

Better Reliability

Using DEF fluid helps create a more reliable vehicle. DEF helps the critical components of a vehicle to run as efficiently as possible. You can know that when you turn the key on and put your car in drive, it’ll get the job done.

Especially now that DEF is standard on diesel-powered vehicles, vehicle and DEF system manufacturers have maximized the reliability of these systems.

Fuel Efficiency

DEF provides an ideal combustion environment in a diesel engine. The result is a more fuel-efficient vehicle.

Some manufacturers state that drivers can experience a 5% increase in fuel efficiency over trucks not using DEF. With the increasing prices at the pump, drivers appreciate every bit of savings they can get.

Keep in Mind: Do Fuel Saver Devices Actually Work? Click the link to find out!

Disadvantages of DEF Fluid

While DEF has some benefits for drivers and the environment, there are some disadvantages. Here are a few crucial cons you should be aware of when using this fluid.

Expensive Repairs

While vehicles using DEF fluid may be more reliable, the repairs can be costly when something goes wrong. Even a minor issue in the system can result in a hefty repair bill of well over $1,000.

If a driver experiences significant damage to their system, it could cost $7,500 to $12,000 to fix. Any repairs the warranty doesn’t cover will likely come from the driver’s bank account.

A man working on repairing damage to his RV after finding out how long def fluid really lasts

Must Keep DEF Fluid in Your Vehicle

Using DEF fluid means another fluid in your vehicle that you’ll have to worry about checking. A vehicle with a DEF system will alert the driver multiple times when they need to put DEF in their tank.

However, if they delay refilling their DEF tank, they’ll find themselves in a difficult situation. These systems will reduce the power and performance of a vehicle and often reduce the maximum speed to five miles per hour. This will be the top speed until the driver refills the DEF reservoir.

Depending on where you’re traveling or driving, finding DEF can be challenging.

The most cost-effective places to get DEF fluid are at big-box retailers like Walmart and pumps in the truck lanes at truck stops. It’s best to regularly fill your DEF tank to avoid running out of DEF while on the road.

Keep in Mind: There are many places you can purchase DEF fluid, but we recommend Avoiding Walmart DEF Fluid!

Risk of Cross-Contamination

A significant risk of using DEF fluid is cross-contamination. This is when a foreign substance somehow gets into your DEF tank and pumps throughout your DEF system.

Any impurities in your DEF system can cause costly damage. The port for filling a DEF tank can be next to the fuel fill port. Drivers could quickly put the wrong fluid in the tank and cause severe and expensive damage to the vehicle.

How Long Does DEF Fluid Last?

The shelf life of DEF fluid is approximately 12 months. However, this depends on where you store the fluid.

Extreme changes in temperature and humidity can drastically reduce the life of the DEF. It would be best to keep DEF in a climate-controlled space at average room temperature.

While it’s best to always have DEF on hand, you want to avoid purchasing so much that it’s sitting for too long. Ensure that any DEF you put into your vehicle is fresh and will set your vehicle up for a smooth adventure.

Blue Def DEF002-2PK Diesel Exhaust Fluid, 2.5 Gallon, 2 Pack
  • One gallon of is used approximately every 300 miles
  • A truck with a 20 gallon DEF tank can go up to 6000 miles between fill-ups
FloTool 10732WR Diesel Exhaust Fluid (DEF) Funnel
  • Designed to fit DEF ports
  • No-mess splash guard

Is DEF Fluid Necessary?

If you’re driving a modern-day diesel-powered vehicle, DEF fluid is essential.

DEF maximizes the power and performance of a vehicle. Drivers who run out of DEF in their vehicle will quickly experience reduced power, speed, and performance. 

What Is DEF Fluid Made Of?

DEF fluid is a mixture of urea and deionized water. It’s typically 32.5% urea and 67.5% deionized water.

Urea is a chemical found in urine, but the urea in DEF is refined. It’s the same chemical many agricultural industries use in fertilizers to help encourage growth in plants and other vegetation.

If your DEF fluid doesn't last long, you can fill it up at a DEF station

Is DEF Fluid Worth It? 

There’s not much better than the purr of a diesel-powered engine. However, older engines were terrible for the environment and created pollution.

We love the power and performance of diesel engines and taking care of the environment. Using DEF can allow a driver to do all the heavy-duty tasks they require of diesel-powered engines without creating more pollution than necessary.

Where do you prefer to get your DEF fluid? 

Last update on 2024-05-27 / Affiliate links / Images from Amazon Product Advertising API

1 comment
  1. I normally fill at stations which have a lot of diesel being pumped. That means the fuel is delivered more often (fresher) and DEF is also fresher. When making a long trip, I’ll care one 2.5 gallon box of DEF just so I have it available. And I’ll use that box to fill the tank near or at the end of the trip. I try to keep the DE at east half filled and always make sure to use the entire contents of the box I carry so there are no issues with contamination or the DEF breaking down.

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