What Is AdBlue Fluid And Do All Diesel Vehicles Need It?
This is the kind of question where we'd better talk about terms before answering it. That's because AdBlue is a brand name for what folks in the United States usually call diesel exhaust fluid — aka DEF. The "AdBlue" name is actually owned by Verband der Automobilindustrie, which translates into the German Automotive Industry Association. The VDA then licenses AdBlue to manufacturers, like BASF, to sell.
Whatever you call it, DEF is a fluid used to help clean up diesel exhaust. It's made from urea and deionized water, and when it meets diesel exhaust gases, it causes a chemical reaction. That, in turn, breaks down harmful nitrogen oxides into nitrogen and water.
As a result, it's definitely required for many diesel vehicles — if you want to meet emissions standards. (Of course, when you consider all the emissions-cheating devices out there, it's clear not everyone does.) The bottom line is that a diesel engine does not need DEF to run; it needs the stuff to run cleaner.
Negating noxious emissions
The current state of clean-air legislation is, well, up in the air in the United States right now. In fact, for some places, emissions standards are a thing of the past. The national picture isn't quite that dark, though. EPA regulations still require most diesel-powered vehicles to limit emissions, and one key method — selective catalytic reduction — requires DEF to operate.
Selective catalytic reduction refers to a situation where the DEF and the exhaust gases meet in the presence of a catalyst. That enhances the chemical reaction that creates nitrogen and water from nitrogen oxide and DEF. Older diesel engines often relied instead on exhaust gas recirculation. Here, the exhaust gases are recirculated into the intake system to lower the temperature of combustion in the engine, helping prevent nitrogen oxide from forming without the need for DEF.
Just keep in mind that the two systems aren't mutually exclusive. The pre-Trump focus on the environment saw some diesel-makers putting serious effort into meeting emissions laws, even to the point of incorporating both selective catalytic reduction and exhaust gas recirculation.
What happens if you don't use DEF in your diesel?
Since DEF is used up when the engine is operating, it's something you have to replace on a routine basis. How often depends on how you drive, since a gallon of DEF is good for about 400 miles of travel, but recent cars and trucks generally have warning lights on the dash to tell you if your DEF tank is getting low. You don't want to let it get too low, either, or it will start affecting performance. Let it run all the way out, and you could be left stranded by the side of the road — despite your engine being just fine.
True, letting your DEF tank hit empty can damage the sensor in that tank that monitors the fluid level, and that can cost some $1,200 to replace. Yet the real issue is that modern diesel vehicles are programmed to only run when they can tell DEF is being used to try to limit emissions. The system may first start by simply limiting how much power you get, but it can also prevent the engine from restarting.
That's why folks participating in the American pastime of coal rolling — where people remove those very emission controls from diesel trucks, letting untreated exhaust gas billow out in black clouds — have to know what a deleted truck is. Now if we could only delete drivers who think that's a good idea.
