Your Guide to AdBlue - What It Is, Who Needs It, and How to Refill It

You all know what diesel fuel is and how it works. It is the stuff used by diesel engines to run, the ones that do not operate with the help of a spark plug, but use compression of air and fuel injection instead.

Diesel fuel came to be thanks to the efforts of a German scientist named Rudolf Diesel, who needed it for the compression ignition engine he worked on in the early 1890s. Since then, the fuel has evolved a bit, was standardized, and for a long time it was the preferred means of propulsion for many of the cars  and drivers of this world.

Diesel came (and still comes) with several advantages over gasoline. The one people cared for the most is its price – diesel has traditionally been cheaper than gasoline (that's no longer the case in our day and age), and that turned it into the fuel of choice for fleet operators, but also for a large segment of the population.

Then, diesel delivers up to 30 percent better fuel economy than gasoline, depending on the engine that uses it and way people drive. The lack of spark plugs makes the engines that use the stuff easier to maintain, and they also have a tendency to last longer than gasoline powertrains.

There are, of course, disadvantages to operating a diesel-fueled engine, and the biggest of them all has to do with emissions. Compared to gasoline engines, the ones that burn diesel are far more harmful.

Technically speaking, they release a tad less carbon dioxide, but they make that up by throwing into the air toxic particulate matter. The list of such substances, which is quite long, includes nitrogen dioxide, nitrogen oxide, carbon oxide, sulfur dioxide, and even soot.

Attempts made over the years to reduce the amount of harmful substances emitted by diesel engines included everything from deploying new bits of hardware, like catalytic converters, to creating new substances that can be mixed with the fuel and tame it. One such substance is called commercially AdBlue, and that’s what we're here to discuss now.

What is AdBlue (aka diesel exhaust fluid - DEF)

In a nutshell, AdBlue is a liquid substance that can be used in diesel engines with selective catalytic reduction. It's main purpose is to help cars cut back on the amount of nitrogen oxide (NOx) emissions they release. The stuff is a mix of urea (32.5 percent) and urea (67.5 percent), and it works like a sort of solvent.

The term AdBlue was coined by the German Association of the Automotive Industry (VDA) to please the eyes and ears of the general public. It is the term most people now use to designate any kind of diesel exhaust fluid (DEF). It's not the only term used for the substance, as in some places DEF is marketed as AUS 32.

AdBlue is a liquid that goes into its own separate tank (so, not in the same place you put your fuel). Despite its name, it's not blue, but colorless, non-toxic, and comes in plastic bottles you can purchase from the gas station and elsewhere.

The fluid is sprayed by means of an injector right into the exhaust system, and once in there, the droplets do a wonderful job, through a chemical reaction, at neutralizing some of the harmful emissions resulting from burning fuel.

It does this by breaking down soot and unburnt fuel and turning them into water and nitrogen, both of which are harmless to people and the environment.

The AdBlue idea has first been adopted by buses and trucks, which have been using it for some time. Since 2015, all new diesel passenger cars are required to have an AdBlue system.

AdBlue refilling

Like most other fluids that go into a car, the AdBlue does not last forever. That means you'll have to top it up from time to time, either by turning to help from a dealership, or by simply doing it yourself. It's not that complicated, as the procedure is quite similar to that of fueling the car – in fact, generally speaking, the cap for the AdBlue tank can be found right next to the fuel one.

How often do you need to replace it? Well, AdBlue consumption levels vary depending on the car, the particular after-treatment system of the exhaust gasses, but also on driving style and driving conditions.

A vehicle that is being driven hard, but also a car that's only driven in start-stop traffic conditions, might have higher AdBlue consumption levels. A vehicle that drives a good mix of city and highway miles will see lower consumption levels. But even if you're driving like an old lady, you'll still need to refill that small tank from time to time.

The average consumption levels for the AdBlue stands at about 0.26 gallons (one liter) per 750 miles (1,200 km). It's quite a lot, but will still require you to constantly keep tabs on the stuff, especially if you are a frequent traveler.

How will you know when it's time to fill it up? All cars with the AdBlue system have a dashboard warning light that tells you when the fluid is running low. Typically, this light will inform you that the fluid level is getting low starting a few thousand miles before the refill is necessary, so you'll have plenty of time to get some AdBlue before your car needs it.

Under no circumstance should you ignore the warning light. Like it or not, AdBlue is essential to the operation of modern-day cars, and without it driving a diesel is almost impossible.

I say almost because the car will technically still drive, but it will do so in limp mode, as the vehicle is trying to cut down emissions some other way. As you know, limp means anything from limited speed to the turning off of the air conditioning and sound system.

The cherry on the cake, if for some reason you are forced to stop but still don't refill the AdBlue, cars will generally refuse to start, especially when the tank is completely empty.

So, as soon as your vehicle notifies you that you must refill your AdBlue tank, it is time to do that. As said, you can choose to do that by turning to specialized help, but given how this is something you could easily do yourself, and at a lower cost, here's how you can do that.

How to refill the AdBlue tank

Before getting into it, please follow the instructions below and perform the minimal work required only if you feel comfortable with it, while also observing a high degree of caution.

The very first thing you need to do is purchase the AdBlue. You can do that from a gas station or online, and there's no need to look for a certain specification – all AdBlues, no matter their maker, are the same.

To know how much of it to buy, you'll need to look at the car's manual, as that's where you’ll find info on the capacity of your AdBlue container. If you do not know how much AdBlue you need for your car, you will have to look it up online. Once you figure out how much AdBlue you need, look for the refill procedure specific to your vehicle.

Assuming you already are in possession of the magical AdBlue and you know how much of it you need, the next thing you should do is locate the cap for the fluid's tank. As said, generally these things are to be found next to the cap for the fuel tank (in that case, make sure you choose the right one), but in some cases there could be another position for them.

BMW, for instance, has placed the AdBlue tank and its cap under the hood, and there are even cases when it can be found in the trunk.

An important thing to keep in mind is that only vehicles that run the AdBlue technology need AdBlue. What that means is that if there is no AdBlue cap anywhere on your car, you should not use the fluid.

Unless you refill it with the manufacturer-designed containers, a funnel will be necessary for the top up with AdBlue. Some vehicles have a special AdBlue filler nozzle to prevent spills. If your car has one of these, you might need to get a refill bottle from your vehicle manufacturer, along with a few extra liters of AdBlue from an independent brand.

The trick is that you can modify the anti-spill refill bottle sold by the manufacturer of the vehicle to use as a funnel. Once you do this, you can refill your AdBlue on your own without any trouble.

In some countries, gas stations do offer AdBlue at the pump, but these stations are rare and usually target truck drivers, who require serious amounts of AdBlue.

For the average Joes, the substance comes in small recipients, but it can also be had in big, 2.6-gallon (ten liters) canisters. You could feel tempted to buy such large quantities, but you'd better not. AdBlue has a rather short shelf life and is widely available, so stocking up on large quantities is not a good idea.

It is recommended only to buy as much AdBlue as you need to refill, and to avoid storing the excess amount. Keep in mind that AdBlue and tends to lose purity once it comes in contact with air, and that may end up damaging the emissions control system.

AdBlue dos and don'ts

AdBlue is a wonder substance and, as said, it is not toxic. That doesn't mean, though, you can do whatever you want with it, and it also doesn't mean you can try to fool your car in an effort to make a buck.

Although using AdBlue is simple and straightforward, always make sure you stick to the instructions on the bottle, but also the ones provided by the car manufacturer.

Never ever use anything other than AdBlue (again, it doesn't matter who makes it) to fill the AdBlue tank. Also, don't ever try to dilute the substance in an effort to make more of it.

There's a pretty good chance your car will know you are trying to trick it. Pretty much all of the cars that have this exhaust technology come with a urea concentration sensor, so they'll instantly know about the trick.

If you choose to ignore the warnings, you may end up damaging your car. Friendly warning: you should never use urine either, despite its concentration of urea.

AdBlue is technically not dangerous to objects, and it means that, unless you use something else instead of the actual AdBlue solution, or if you spill the stuff on your car in a serious manner, there's no reason to void your car warranty because you've refilled your AdBlue tank.

Be careful not to spill it everywhere, though, as it may end up corroding some metals, especially when used improperly and for long periods of time. Make sure you store and transport the stuff with care.

The non-toxic nature of the fluid means it's not dangerous to humans, but under no circumstance should you drink the stuff. If you get it on your skin, make sure to rinse thoroughly.

Last but not least, and perhaps the most important thing of all, we cannot stress the importance of not pouring AdBlue in the fuel tank, as it will severely damage your vehicle.

 It's a mistake that could happen, given the close proximity of the two caps, but one that could easily be avoided with just a trace of care and some sight skills: the AdBlue cap is usually blue, and it says AdBlue all over it.

Below, we've included a video detailing how the AdBlue refilling procedure should be done.