AdBlue/DEF 101 – FAQ & What You Need To KnoW

Diesel Exhaust Fluid is commonly referred to as “DEF” for short or by its trade name, AdBlue.  In this article we’ll review what DEF is and what you need to know about it.

Here are the most common questions we hear regarding Diesel Exhaust Fluid

  • Is it DEF or AdBlue? – Both are correct.  AdBlue is just a brand name for DEF, some manufacturers use the AdBlue label while some do not – PEAK for instance calls their product BlueDEF.  Using the term “AdBlue” to refer to DEF is similar to saying “Kleenex” when you are referring to a tissue.
  • Do I need to buy the AdBlue version? – No, DEF is actually a standardized fluid, ISO 22241.  As long as the fluid you purchase is marked “AdBlue” or has ISO 22241 approval on it it will be approved for your vehicle.
  • Do I need to buy it at the dealer? – Absolutely not.  DEF is widely available now.  You can find it at most chain parts stores, truck stops and even online (  Some truck stops actually have DEF pumps!
  • How often do I need to refill DEF/AdBlue? – DEF range can vary between models and driving habits.  DEF usage is tied to fuel usage – the more fuel you use the more DEF will be used as well.  Most vehicles have DEF tanks that are sized for 10,000 miles of range on average.  If you tow frequently your DEF usage will go up as your fuel consumption also goes up.  
  • What does DEF do? DEF is injected into the exhaust system in order to remove NOx gasses from the vehicle’s emissions.
  • Does DEF expire/go bad? – Yes, actually, DEF has a shelf life which is pretty short.  Exposure to sunlight and high temperature can accelerate the breakdown of the fluid.  If your DEF has gone bad your vehicle will throw an emissions check engine code.
  • Does DEF freeze? – Yes, DEF freezes a few degrees below 32F/0C.  This means that during the winter the DEF in your vehicle will freeze.  However, DEF tanks have built-in high wattage heaters to unfreeze DEF.  These heaters do fail from time to time and will need to be replaced if failed.
  • Is DEF toxic? – No, DEF is actually a totally safe, organic fluid.  You shouldn’t drink it, but it isn’t toxic.  It does leave a nasty crust when it dries, though, so try not to spill it!

Do you have questions about DEF/AdBlue?  Let us know in the comments below…

  1. […] What is AdBlue?  Read more in our AdBlue/DEF 101 Article. […]


  2. Q: Is DEF corrosive?
    A: Yes. Avoid contact with your skin or the car’s paint.


    1. While it is technically corrosive it is not a very strong corrosive and is not hazardous. You can have it on your skin without injury, though it does get itchy so you should wash your hands after exposure. It will not damage paint, though it may stain clothing and will leave a white crystalized residue behind when dried – though that can be easily washed off with water.


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