How long does a bottle of diesel exhaust fluid (DEF) last once opened? – Jalopnik

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The government’s strict emissions limits for internal combustion vehicles have pushed automakers to develop technologies that keep their engines compliant while producing large amounts of power. Diesel Exhaust Fluid (DEF) is an important component designed to reduce nitrogen oxide emissions from diesel engines. DEF, also known as AdBlue, is a solution of deionized water and urea, stored in a separate tank from the fuel and automatically injected into the engine exhaust stream after combustion.

There, DEF turns into ammonia and isocyanic acid, which chemically react with exhaust gases such as nitrous oxide and break them down into harmless substances such as nitrogen, water vapor and carbon dioxide. The capacity of your DEF tank varies depending on your vehicle, but typically ranges from five to 25 gallons. The tank must be refilled from time to time as vehicles use one liter of DEF for every 50 liters of diesel fuel burned.

Although you can find DEF at some gas stations, it is often sold in containers at truck stops, which cannot be found everywhere. That’s why drivers often buy an extra can and save it for when they need it and find it out of reach. Unopened DEF typically lasts about two years from the time it was made before it spoils. But once you open it and there is an excess, it is expected to last in the bottle for about a year before breaking down, provided it is stored properly: sealed and in a cool, dry place, away from sunlight (ideally between 50 and 86 degrees).

Although DEF is made for a long shelf life, letting it sit for many months before using it may not be the best choice because improper sealing or significant headspace in the can can cause it to evaporate and crystallize. But you can tell if your DEF has gone bad just by looking at it, as contaminated DEF looks cloudy, discolored, or crystallized instead of clear, or is thick instead of flowing easily.

This is your cue to throw away the old DEF. And because it’s so reasonably priced, you can get 2.5 liters BlueDEF for about $21 – it doesn’t hurt to always use a new one instead of settling for old fluid, which may be less effective and even damage your selective catalytic reduction system. The great thing is that your vehicle will display a warning light to remind you to refill the DEF tank well before it runs empty. This reduces the chance of being caught off guard and eliminates the need to carry an opened bottle of DEF with you.

However, if you are storing an already opened DEF for future use, make sure the cap is properly tightened to prevent it from mixing with air or other contaminants such as dust. And avoid storing near the engine or exhaust to prevent degradation from heat exposure. On the other hand, all of this assumes you keep your emissions systems intact and aren’t considering removing your diesel truck.