Water In Diesel Fuel


There are several dangers associated with diesel-fueled machinery, but water in diesel fuel is one of the most serious. Diesel fuel, which is less refined than gasoline and therefore holds a greater amount of water in suspension, is the exception.

When used in water separators, this water might cause major issues. Fuel injector tips can rupture as a result of this, requiring costly repairs. Slugs of water in the fuel, on the other hand, can cause an abrupt cooling of the engine, which could lead to a reduction in engine life.

Water in diesel

There are two forms of water in diesel fuel: water in solution and free water. Low quantities of water can be found in fuel, which is why it is referred to as “water.” Parts per million (ppm) are the measurements used to describe these extremely low water concentrations.

Dissolved water can be found in fuel for a variety of reasons. Gasoline temperature and water condensation in a fuel tank tank and fuel system are a few of the factors that contribute to keeping water in solution.

A variety of variables, including condensation in fuel tanks, incorrect handling, and weather conditions can contribute to water contamination in fuel. Water should be removed from diesel fuel prior to solid particulate filtering to reduce damage.

Diesel fuel tanks getting water

Because diesel has no vapor pressure to displace air, water condensation occurs in fuel tank. The air expands and is sucked out of a warm gasoline tank. At night, as the tank cools, damp air is sucked back into it, where it condenses and drips.

This is one of the reasons why it’s important to keep your fuel above ground tank full at all times. An open fill port, a faulty tank, or rain entering an open drum can all introduce more water into a fuel system. Alternatively, it might be moved from a contaminated water tank to the new one.

Diesel fuel tanks getting water

Diesel fuel system problems induced by water


Water in diesel fuel systems can lead to a wide range of issues. When exposed to water, steel and iron rust, releasing iron oxide particles into the air. Fuel filter can quickly become clogged with rust particles. The cooler tank walls stars to rust.

It’s possible for rust particles as small as one micron in size to get through fuel filter and into injectors, where they score fresh metal surfaces and disrupt spray patterns.


Soil bacteria thrive in stagnant water, such as those found at the bottom of a gasoline tank. Tank holes and dispensing allow microorganisms to enter. Diesel fuel can be a food source for bacteria in a moist environment because of the interface formed by the fuel and water.

Bacteria and fungi can thrive in fuel that contains water. These microorganisms produce slime, which clogs filters and fouls fuel injectors as it travels through the fuel system. They can corrode hot metal surfaces because of the acids they create.

These microorganisms produce a slime coating that can clog gasoline filters and disseminate bacteria throughout the entire fuel system. This can be quite dangerous. A black layer of moist gel will cover the upstream surface of a fuel filter that has become clogged with bacterial slime.

As a waste product, living bacteria release acids, which corrode and damage fuel system components even more.

Diesel fuel contaminated by microbial growth (bacteria and fungus) is a common yet dangerous occurrence. It’s difficult to get rid of them once they’ve multiplied and colonized the area. Because bacteria exist at the water-diesel interface, water is a necessity for them to develop and multiply.

A tank with less water in it has a lower chance of producing a problem. Once the microorganisms are in there, they start creating acids that degrade gasoline quality and damage tanks. They also clog filters and remain until you use a biocide to kill them.

Diesel fuel system problems induced by water

Is there a way to keep water out of my diesel fuel tank?

Rainwater entering your diesel tank through an open fill point, vent, or condensation is a common cause of water in fuel. Because fuel tank air expands when temperatures rise, water drops form on the tank walls because cold air is pulled in and forced out of the tank vent.

While water contamination can occur with any fuel, today’s diesel is more troublesome due to the higher percentage of bio-content. Water content is a natural component of biodiesel. Due to its hygroscopic nature (it attracts and holds onto water), it’s considerably more vulnerable to contamination than usual.

Signs that diesel fuel has been tainted

It’s possible to test your fuel or use a paste that detects water in the bottom of a container if you store it on-site and fear it’s contaminated with water. Tank owners should be aware of the symptoms of tainted fuel, though. Do you have a strategy for finding what you’re looking for?

Your fuel’s color and appearance

When the water content in diesel surpasses the amount that the fuel can handle, the fuel’s appearance can alter.

It’s free water, and as the name implies, it’s separate from the fuel in the tank. Water forms a layer beneath gasoline when it sinks to the tank’s bottom from the additive. Diesel bug thrives under these conditions, posing a threat to your machinery, cars, and engines.

Suspended water

Your foggy diesel fuel is caused by a form of water pollution known as suspended water. In order to make it appear hazy, suspended water is mixed in with the fuel and is essentially mixed in with the fuel. Free water begins to leak from the bottom of the tank as the diesel fills up and can no longer retain it.

Emulsified water

The water content can become entirely emulsified as the gasoline travels through pumps and filters due to pressure changes, agitation, and strong cavitation. In this area, the fuel molecules and water content are nearly indistinguishable.

Changing fuel filters on a regular basis

The first sign of polluted fuel is that your fuel filters are filling up faster than usual when contamination becomes a problem.

Filters are made to catch and store water, so if you have a lot of water in your fuel, you’ll have to buy new ones more frequently. Filters getting clogged due to unpleasant muck are another possibility.

Decreased lubrication requirements

The diesel fuel’s lubricating qualities are reduced as water passes through and into the injectors. Injection tips are damaged and sensitive fuel systems mechanical components corrode due to galling and early wear.

Removing water from diesel

In the event of contaminated diesel fuel pumping out of a tank, the water is visible as floating droplets that can be easily removed from the fuel with a high-quality fuel/water separator in place.


Without first removing the water, a stable emulsion will form between the diesel fuel and water, making it nearly impossible to extract the water. In this approach, some of the water can be burned, but most of it will collect and erode the fuel system’s delicate components. 

Diesel’s impact on the environment 

Biodiesel is occasionally blended with petroleum for both environmental and economic reasons. Removing water becomes more difficult when biodiesel at a 5 percent concentration.

When biodiesel concentrations above 20%, it becomes practically difficult to separate the diesel fuel from the water. Many primary filtration mechanisms are unable to filter water efficiently, making the engine a target for pump and injector damage, as well as decreased performance.

They are as a result, prior to solid particulate filtering, it is critical to properly remove water from the fuel.

Removing the water from the diesel fuel.

Step 1

Check to see if the diesel has any water in it. Hand-operated bilge pumps can be used to remove a small amount of suspicious gasoline. Allow the fuel to sit for 24 hours in a dark room in a transparent, clean glass container.

Fuel including water will sink to the bottom of the container since diesel is lighter than water. Determine whether or not there is a faint black line separating the water from the diesel. The presence of microbial growth suggests that a biocide must be added.

Step 2

Let the fuel sit for a while so it can settle. For at least a day, refrain from moving the container. Fuel tanks on cars and boats as well as hand-carried fuel cans are all examples of this.

Step 3

If you have a fuel filter, drain the water and re-add it to the system. Fuel-water separators with petcocks should be installed at the bottom of storage containers and diesel engines boat fuel tanks. It’s easy to detect when the water’s gone through the drain because some are transparent. It’s better to over-drain than under-drain.

 Step 4

In tanks without fuel filters, remove water by pumping it out of the bottom. Connect the bilge pump extension hose, making sure you have enough hose to reach the tank’s bottom. Fill the tank to the brim with water and then drain it completely.

Step 5

Pour the diesel slowly through the baja filter into a second container if it is in a hand-carried gasoline can. Include a biocide in the mix. Commercial diesel fuel biocides can be found in auto parts stores, truck stops, and numerous marinas and boating supply stores. When adding biocide to the fuel, follow the manufacturer’s instructions exactly.


A significant issue has arisen with water contamination of diesel fuel, and it needs to be handled right away. Diesel engine need a high-pressure fuel pump with extremely tight tolerances. Any type of contaminant, even water, has the potential to do significant and expensive damage.

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