How To Remove Water From Diesel Fuel

It's not really that difficult to remove water from diesel fuel. We got you covered. This is the ultimate guide on how to get rid of water in diesel fuel.

All diesel holds some water, even if it’s an indescribably low quantity.

Water in your diesel fuel tank could be a real issue (over time). It leads to microbial growth, which rots the metal away and could clog or damage injectors. Over time, it could even lead to a leak.

Thankfully, the amount of water in your diesel is almost always negligible. As well as having contaminated fuel, your car would need to sit – stationary – for a long time before any damage starts being done.

Although water in diesel sounds terrible and scientists have spent years trying to prevent it, it might not be. Some studies have even found that a water-in-fuel emulsion reduces harmful pollution.

There’s a crucial difference to know here. The water in your diesel could be either “free water” or “water-in-fuel” (aka “water-in-solution”). Water-in-fuel is normal and perfectly fine. Free water is an issue.

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How Does Water Get Into Diesel?

Fuel pump

Diesel is a mix of hydrocarbon chains (and additives). It’s refined from crude oil, along with many other things like gasoline and kerosene.

The refining process isn’t 100% efficient. Nothing is. That means there will always be a small amount of contamination. In this case, it’s water.

All diesel holds a tiny percentage of water. Standard low-sulfur diesel holds up to 0.1%. Biodiesel is a bigger culprit, harboring up to 1% water.

It might not sound like much. And it isn’t. This is water-in-fuel and your engine has been built to accommodate it. It will fire into the cylinder as vapor and burn off with the diesel.

Free water (liquid) would, however, be an issue. You need to watch for excess water from your tank to the fuel filter through the fuel lines. It’s here that rust could start to form.

Do I Have Water In My Diesel Car?

Water in bottom of diesel fuel
Water will sink to the bottom of the fuel tank.

The problem doesn’t usually hit civilian passenger vehicles. That’s especially true if you fill up at a standard gas station.

The regulations surrounding diesel quality are simply too strict. For example, EU standard EN 590 allows for “200mg/kg of water” (0.02%). According to a Polish research paper, a standard range for water content in diesel is“0.003 – 0.100% (m/m)”. This is all water-in-fuel.

No matter what vehicle you drive, the best way to check your diesel for free water is to look at the fuel filter. Check your owner’s manual to see where to find this.

Provided you haven’t driven for a day or so, the water will sink to the bottom. You’ll see it when you take the filter out. Be careful not to spill the fuel.

There’s no real way to check the water content in your fuel tank except for some testing paste on a long dipstick. Checking the fuel filter is much easier.

This problem much more commonly affects vehicles in the construction, agriculture, or marine industries.

These vehicles often fill up from above-ground tanks. These tanks are more likely to build up water over time. This water might inadvertently get pumped into their fuel tanks.

It takes a lot of fuel to create a water reserve large enough to start rusting. But vehicle fleets will easily get through thousands of gallons per year.

How To Get Rid Of Water In Diesel

Fuel Tank In Car

As explained, excessive water in a passenger vehicle is very rare. It should only happen if you use unregulated biofuel in your tank.

You probably won’t know about free water in your diesel until a mechanic finds water in your fuel filter. In the meantime, you might get misfires due to broken injectors (in extreme cases).

Once the water’s in your tank, that’s that. You should drop the tank out of the vehicle and flush it.

If enough damage has already been done, you might even want to install a new tank. At the very least, antibacterial substances should be used to remove any traces of the rust- and gunk-creating microbes.

Free water might even have done some severe engine damage.

It’s important to trace the source. Water shouldn’t be in your tank, especially not in a new diesel vehicle. It’s more likely to come from an above-ground filling tank.

The vast majority of any trace amounts of water in your diesel will mix into an emulsion (a temporary mixture). It’ll pass through your engine in small enough quantities to not do any damage.

Alternatively, you could use a diesel additive. This won’t be a long-term fix for any rusting problems, though.

Additives To Remove Water From Diesel Tank

You might have heard of some additives that remove water from diesel (or gas). Some of the most common are made by:

  • CRC Diesel Dry
  • Diesel Force HydroClean
  • ISO-Heet Water Remover & Fuel Line Antifreeze

These don’t remove water, per se. The additives are often purified isopropanol (also known as isopropyl alcohol or rubbing alcohol). Other chemicals are added for further benefits.

Isopropanol is a hydrocarbon chain with three carbon atoms. It bonds with the water (H2O), holding the molecules within its structure.

The water can now pass through the engine as part of the isopropanol. The water doesn’t turn into diesel (now there’s a trick that would be worth seeing!) – but it’s now part of a flammable liquid.

The isopropyl alcohol hydrocarbon isn’t exactly perfect for your engine, but it’s much better than water. Since it’s the same type of hydrocarbon as diesel, it mixes in with your fuel.

After pouring in the isopropanol additive, wait for a few hours. It sinks to the bottom of the tank and chemically bonds with any water.

Ensure you add the correct ratio of isopropyl alcohol to water.

Can You Add Rubbing Alcohol To Diesel To Get Rid Of Water?

Diesel Additive

Make sure you buy a proper additive.

This contains pure isopropanol. Rubbing alcohol off the shelf usually contains about 70% isopropyl alcohol and 30% water. The range can vary between 60% and 90% alcohol.

That’s because higher alcohol concentrations don’t yield particularly better anti-microbial results. It’s a waste of money, so pharmaceutical companies top it up with water.

Therefore, adding a rubbing alcohol solution to your diesel tank actually adds more water. Well, if ever there were a futile exercise…

Conclusion

Diesel fuel nozzle

In summary, this issue usually affects fleet vehicles’ filling tanks. It’s most likely to impact those that store diesel on-site without proper maintenance.

If you have an unusually high amount of free water in your car’s diesel tank, it probably came from one of these.

Diesel additives should be added to a storage tank to bond with any free water. Do this pre-emptively – before the rust even has a chance.

If you find free water in a vehicle’s fuel tank, drop and clean it. If necessary, replace it.

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Benjamin Kitchen

Ben is an automotive author from England. With experience in a fast-fit garage, he's an IMI-qualified light vehicle technician. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa – it may have a tiny engine, but in eight years it's never once let him down!

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