Should I Keep My DEF Tank Full in Equipment and Trucks?

Almost all diesel equipment is currently fitted with the DEF system. This is a Diesel Exhaust Fluid system that supplies special urea-based liquid into the exhaust system to or at least reduce NOx in the exhaust gas. The system is pretty straightforward but its introduction in all diesel equipment forms a lot of questions that people just can't answer because the technology is relatively new.

Today, we'll tell you whether it's a good idea to keep your DEF tank full. We'll also figure out some surprising factors that can cause problems with a full tank of DEF. Also, in our article, we'll give recommendations to follow for owners of trucks and equipment with modern diesel engines that are fitted with DEF systems.

Here's what we'll be talking about:

• Why adding DEF regularly is so important for your equipment or transport?
• How much DEF can a truck or some other equipment use?
• What's the average size of the DEF tank in modern equipment?
• Is keeping a full DEF tank a good idea?
• How can you check the amount of DEF in the tank?

Let's get started!

Why should you always add DEF if your equipment has this system?

Well, technologies become more complex and we don't always understand the purpose of certain new things. Like DEF, for example. If we don't take all the purposes of this system, it seems like another pain in the neck for business owners and equipment operators, truck drivers, etc. In older trucks, you should have made sure that it had some fuel in the tank and that you were good to go. But now you should also check DEF.

Businesses hate spending money on additional fluids like DEF, so they are also not really fond of this idea. And this leads to the question: Should I at all add this DEF? Or can my equipment work well without it? Unfortunately, the answer is too complex and not really positive.

Here's what you should consider:

• the DEF system is programmed into the ECU and other units of your vehicle, so when something goes wrong, your equipment will go crazy;
• in most cases, your engine will go to limp mode (derate) and will work in the limited power supply or with RPM limitation until you add DEF again;
• also, the overall efficiency of the engine may go down because some sensors will send the wrong signals to the ECU;
• the exhaust will become more toxic, the amount of NOx in it will certainly be escalating and this may lead to problems;
• one more issue is that when you add DEF, the sensors may need resetting with code scanners or other professional equipment.

As you see, the absence of DEF in the tank may lead to issues. In some cases, it will result in the same problems as clogged DPF. The engine will derate and you'll be able to drive your truck at a slow speed only or use your equipment for a very limited range of tasks. This is bad for business and for your plans.

On the other hand, you can reprogram the equipment and basically delete the DEF system. It's physically possible but will result in a huge ecology fine the next time your equipment will need to go through the emission test. So, you just have to add that DEF whatever you think about it. Now, we can turn to the main question of our article.

Should I keep the full tank of DEF in my equipment or truck?

DEF is gradually used by the diesel engine in small amounts. This means that if you are going to use your equipment in a remote area where you don't have access to fuel pumps and other places where you can buy DEF, you will naturally want to get as much DEF as possible making it the full tank.

And here you will have one big possible problem: the temperature. DEF consists of water and urea and basically, this mixture can easily freeze. When it freezes, just like water, it adds about 7% of its volume. If you fill the full tank of DEF and leave the truck or equipment outside when it's freezing, you can find your DEF tank torn apart because of frozen liquid.

Once it's frozen, it may stop working for a while. But once you start the engine and the exhaust pipe becomes warm, the DEF will get back to its normal condition. As specialists say, freezing will not affect the quality of DEF fluid, so you may not worry about that.

The only thing you should really worry about is your plastic tank that holds DEF in your vehicle or equipment. If DEF freezes when the tank is full, it will obviously destroy the tank and you will have to spend some money.

How to avoid DEF tank problems?

It may sound easy - never fill up the DEF tank to the full. But in most cases, you don't see this DEF tank. You see the filler neck and can't visually check the amount of DEF inside the tank. Usually, you may stop filling it up when some DEF is visible in the neck. And it's OK for summer weather. But if there is a chance that your equipment is going to spend some time outside in the freezing weather, better avoid this.

If you don't have any possible ways to check the level of DEF in your tank, the best solution is to add a little DEF and sometimes even wait till the warning light goes on. Yes, you may have problems with that warning light reset in the future. But it's much better than repairing your equipment and installing the new DEF tank.

How to check the level of DEF in your equipment or truck?

In most modern vehicles and equipment, you will find a special gauge or light bars showing the amount of DEF in the tank. This is the easiest way to check the amount of DEF in the tank - just look at the gauge or light bars and detect whether you should add some DEF or not.

But if you don't have this gauge or it's broken, there are some other ways:

• Wait till the warning light is on. If your equipment has a warning system about the low DEF level, you will see the light on and maybe some message on the dash forcing you to add DEF. At this point, you may be sure that there is about 10% of DEF in the tank.
• Wait till the engine loses its performance. This is a very extreme way but still possible. So, if warning lights don't work or aren't meant to be there in your equipment, wait until the engine derates, and then you are sure that there is no DEF in the tank.
• Add DEF to the full and keep the engine on. If you are going to work on your equipment or drive your truck, you may add DEF to the full tank and keep driving or working. Also, learn how much DEF your equipment takes per hour or per 100 miles. This will help you make sure that the tank is not full when you park your vehicle or equipment for a night.

So, these are the ways you can use to make sure that your truck or equipment doesn't have the full tank of DEF. Remember that you will actually need this in those cases only when your equipment is going to spend more than one hour with the engine off outside under freezing weather. Otherwise, you may calmly keep the full tank of DEF without any consequences.

How much DEF will your engine take per hour or per 100 miles?

There are different methods to calculate the consumption of DEF in your vehicle or equipment. The most precise figure may be given in the owner's manual, so just find this section and read the manufacturer's data on this.

If you can't or just don't want to find this information, you may use rough estimates that are true for almost all diesel engines:

• Your equipment or truck will use 2-3% of DEF to 100% of fuel. So, every 100 gallons of diesel fuel will take between 2 and 3 gallons of DEF. Now it's not that hard to count if you know the fuel consumption.
• One gallon of DEF will last about 350-450 miles in an average heavy-duty pickup truck and about 300-350 miles in a semi truck. This is not the most precise figure but it allows you to count it all up at least approximately.
• When it comes to heavy equipment, the best way to check DEF consumption is to count it up according to fuel consumption. It's impossible to give any estimates for 1 hour because engines are completely different.

Final words

You now know that leaving a truck or some equipment with the full tank of DEF outside is not the best idea, especially for winter weather. You should make sure that DEF won't freeze inside the tank and won't lead to problems. Just use the tips in this article to make sure you are OK and don't kill your equipment with your own hands.