What Happens When You Put DEF in a Diesel Tank?

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A man putting def in his diesel tank

Nobody is perfect, and everyone makes a mistake occasionally. However, some mistakes are bigger and more expensive than others.

If you’re not careful, you could accidentally cost yourself a pretty penny in seconds. One mistake diesel drivers make is accidentally putting DEF in their diesel tank. So what happens when you put DEF in a diesel tank?

We’ll take a look at what happens to your vehicle and why you should avoid putting DEF in your vehicle’s diesel tank. Let’s get started!

What Is DEF?

DEF is an acronym for diesel exhaust fluid. This fluid helps to reduce the number of harmful emissions that diesel engines create and release into the environment.

The Environmental Protection Agency (EPA) implemented new diesel vehicle standards in 2010, which require all diesel engines to use DEF. 

There are only two ingredients in DEF; urea and deionized water. DEF must contain 32.5% pure urea, which is responsible for converting harmful gasses into a cleaner and more environmentally friendly exhaust.

If a vehicle runs out of DEF, the power and performance will significantly decline, and the systems could prevent the vehicle from starting.

Close up of a person putting DEF in their tank next to their diesel tank

Can DEF Ruin a Diesel Engine?

DEF is a very corrosive substance and will wreak havoc on an engine and the various components in your fuel system.

If you catch it in time, you can save your engine and many pieces from requiring a complete replacement.

However, it doesn’t take long to ruin your motor if DEF gets into it. Even the slightest bit of DEF can quickly cause severe damage.

What Happens When You Put DEF in a Diesel Tank?

If you put DEF in a diesel tank, it will only take minutes before you start noticing issues with your vehicle. The DEF will gum up the various components in the vehicle’s fuel system, and ultimately the DEF will begin to crystallize to sensitive parts in your vehicle.

The vehicle may run with no issues for a few minutes, but it will likely throw in the towel once the DEF starts clogging the parts. Once this happens, you must immediately get your vehicle to a trained professional to start the repair process.

What to Do if You Put DEF in a Diesel Tank

If you accidentally put DEF in a diesel tank, there are several things that you must do to get back on the road.

Let’s see what you’ll need to do if you make this costly mistake.

Do Not Start the Vehicle

Your best bet is to catch your mistake before you start your vehicle. Any foreign substance getting into your diesel tank is a significant issue, but you significantly reduce the damage and repair costs if you do not start the vehicle.

If you can keep the DEF contained to your fuel tank, a mechanic will need to drop the fuel tank and thoroughly clean it.

This can be expensive, but not nearly as costly as replacing a significant amount of your fuel system.

Sadly, many drivers who make this mistake aren’t paying attention when filling their DEF tank. They end up not realizing their mistake until they’ve started their vehicle and there’s already damage.

So ensure you’re paying attention and catch your mistake as soon as possible.

Call a Tow Truck

Once DEF or any other foreign substance is in your fuel tank, you shouldn’t attempt to drive your vehicle.

Starting your vehicle is bad enough, but moving it a short distance will accelerate the damage. You may need to call your insurance provider to help secure a tow truck for your vehicle.

Communicate with the tow company if you’re driving a big, beefy truck or are towing a trailer. Not all tow trucks can handle towing dually trucks, and you might need to devise a plan for storing your trailer.

Keep in Mind: Accidents happen while on the road and Good Sam Roadside Assistance may be a worth getting for peace of mind!

An RV being towed after  putting def in diesel tank

Take It to an Experienced Mechanic

DEF in a diesel tank is not a repair you can likely do yourself. You must eliminate any remaining DEF in the fuel system and clean any crystalized remains from every nook and cranny in your system.

An experienced mechanic will likely have the skills and tools to disassemble, replace any necessary parts, and reassemble your vehicle as quickly and efficiently as possible.

If you have a trusted mechanic, use them. However, not all shops or mechanics can handle a massive and exhaustive repair on a vehicle. Only trust your vehicle in the hands of a qualified and knowledgeable mechanic.

A car being repaired at the mechanics after putting def in a diesel tank

Be Ready for a Massive Repair Bill

There’s no easy way to say this, but it will cost you if you put DEF in your diesel tank. Repairs can easily cost $10,000+ as parts and labor are equally expensive.

If there are any mistakes you want to avoid making, putting DEF in a diesel tank is likely one of them. You’ll want to brace yourself when the mechanic delivers the repair estimate.

Learn from Your Mistake

The worst error you can make is not learning from your mistakes. Making mistakes is a normal part of life, but you must learn from them if you don’t want to repeat them.

Take this as an opportunity to implement safeguards to protect yourself from future errors. Making this mistake once is bad enough, but repeating it will likely leave you swearing off owning a diesel vehicle.

Pro Tip: Do you know what a DEF Head Is? It’s something all RVers should know!

Does Insurance Cover DEF in Diesel Tank?

DEF in diesel tanks is not a cheap repair, and you’ll likely be in for a shock when the mechanic delivers the bill. Most insurance policies do not cover what they describe as “misfuelling.”

It doesn’t matter whether you put gasoline, DEF, or another substance into your diesel tank. You’ll likely be footing the bill.

Some high-coverage policies and additional mechanical breakdown coverages will cover these issues.

However, most drivers do not have these policies and have no protection from the expenses associated with these mistakes.

A man on the phone with his insurance after putting def in his diesel tank

DEF in a Diesel Tank Is Not Good

There’s no way around it; DEF in your diesel tank is not a good thing. It’ll destroy your engine and potentially leave you stranded. Once you get your vehicle to a mechanic, your vehicle will be out of commission for some time.

To make matters worse, you’ll likely need to pay the bill as insurance policies don’t cover the repair costs. So keep DEF out of your diesel tank, and you’ll avoid making a stressful and costly mistake. 

Have you ever put the wrong fuel in your tank?

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