How Water Gets into Diesel Fuel and How to Remove It
Diesel fuel is the lifeblood of heavy-duty trucks and critical engine components. Ensuring its purity and efficiency is essential for smooth engine operation and longevity. One often overlooked issue that can compromise diesel fuel quality is water contamination. Water in diesel fuel can result in rust particles entering the fuel, promote the growth of bacteria and microorganisms, and, more directly, cause premature wear and corrosion in fuel injectors and other engine parts.
Water contamination became a critical issue after we began using ultra-low sulfur diesel because it attracts more water and is less resistant to microbial growth than previous diesel fuels. Moreover, modern diesel fuel systems are less forgiving of water in the fuel, so it is more important than ever to minimize the opportunity for water to enter a truck’s fuel tank and to keep any water that does enter the tank from reaching the engine.
In this blog post, we’ll explore common ways water infiltrates diesel fuel and discuss methods for removing it.
It may surprise you, but water and diesel fuel are more connected than many realize. Diesel fuel has hygroscopic qualities, meaning it attracts and absorbs moisture from the air at the molecular level, so it almost always contains some water. The key is to minimize the water level by managing the more substantial sources of water contamination and filtering out the remaining water to maximize fuel efficiency and protect your engine. Let’s dive into how water can infiltrate your diesel fuel and what you can do to prevent it.
Most fuel retailers and distributors use water-detecting filters in their dispensing equipment to prevent water from entering your fuel system. However, these filters are effective only when adequately maintained. When these filters become saturated, they may allow water to be dispensed with the fuel. To safeguard against this problem, always buy your diesel fuel from reputable sources with well-maintained systems to minimize the risk of water contamination.
Water can find its way into diesel fuel through other means, including leaky storage tanks or human error. Poor or degraded tank seals can allow water into storage tanks, and human errors such as leaving a fuel tank cap off also invite water contamination. Human error plays a significant role in water entering a fuel tank, so emphasizing the importance of proper fueling procedures and maintenance should be a critical issue for fleets and independent truckers alike.
Another often-overlooked source of water contamination is condensation. Condensation can occur in storage tanks, especially in above-ground tanks, and in truck fuel tanks. Some condensation results from everyday temperature fluctuations, but the more significant challenge is operating the truck and drawing down the fuel in the tank. Unlike gasoline, diesel fuel does not create vapor pressure in the tank to displace air, resulting in air entering the tank as the fuel draws down during operation. Often, the air is drawn into the tank while operating in warmer and more humid conditions. Later, when the temperature inside the fuel tank becomes colder than the ambient air, condensation forms inside the tank. This condensation becomes free water that can enter your engine’s injection system if not removed beforehand. Of course, one means of reducing condensation is to top off the tank before parking it.
Removing as much of the water content as possible is crucial to ensure the purity of your diesel fuel and prevent free water from infiltrating your engine’s injection system. The best method to accomplish this goal is to use a high-quality filtration system that effectively separates air and water from the fuel entering your engine. You can achieve both using the AirDog® FPII system, which passes the fuel through a water separator before sending it to a particulate filter. Importantly, AirDog® recently introduced a new generation water separator, the PureFlow Technologies WS200-HS Water Separator/Pre-Filter, to maximize the system’s overall performance.
Our previous-generation water separator used a 144-micron wire mesh screen to remove water from the fuel before sending it to the AirDog® Champ™ High-Pressure Fuel Air Separator, which filters particulates to 6 microns. Our new PureFlow Technologies WS200-HS Water Separator/Pre-Filter uses Hydrosorb media to achieve an impressive water removal efficiency of over 99%. It also filters particulates to 30 microns before passing the fuel onto the second stage, the 6-micron particulate filter.
The new water separator displays excellent performance, but like many systems, proper maintenance must occur to achieve that performance. As in the past, the particulate filter has a 35- to 40,000-mile change interval. However, rather than reusing the water separator as in the past, the new water separator is replaced at the same time as the particulate filter. Doing so allows the system to achieve unparalleled water separation levels that reduce engine wear and tear.
Water in fuel tank issues can occur in any diesel engine, from everyday pickups to military vehicles. Water inside a gas tank or water in the gas can result from condensation, poor fuel storage, or contaminated supply lines. In a diesel in tank scenario, moisture mixes with fuel, causing corrosion, reduced efficiency, and even injector damage. The problem traces back to Rudolf Diesel’s original design, which never accounted for today’s low sulfur diesel (ULSD) formulations that can absorb more water. In the United States, even a small amount of water in the tank can cause symptoms of water in your engine such as rough idling, smoke, or stalling. Whether your vehicle runs on diesel fuel diesel or fuel oil, solutions include proper storage, regular draining, and fuel additives designed to disperse or remove moisture. Detecting and addressing excess water in the tank early helps prevent costly repairs.
There are many points at which water can enter diesel fuel, so it is essential to take the preventive measures needed to avoid fuel contamination, including practicing proper fueling procedures. Doing so will help maintain the efficiency and longevity of your heavy-duty truck’s engine. Still, water can enter your fuel despite following the strictest guidelines, so a critical step is investing in a top-tier filtration system to keep your engine running smoothly and protect it from the adverse effects of water-contaminated fuel.
Finding water in fuel tank situations is more common than most diesel owners realize, and it can happen in everything from daily drivers to military vehicles. Water inside gas tank or water in the gas problems can start from condensation, poor fuel storage, or contaminated fuel at the pump. When diesel in tank contains moisture, corrosion, injector damage, and fuel system failure can follow quickly.
Even the original Rudolf Diesel design didn’t account for today’s sulfur diesel ULSD fuels, which absorb water more easily. In the United States, ULSD is standard, meaning the risk of water in the tank is something every owner should understand. Whether you’re running on diesel fuel diesel or fuel oil, the symptoms of water contamination may include rough starts, smoke, reduced power, or stalling.
To address water contamination, start with prevention: regular fuel system inspections, keeping your gas tank sealed and topped off to reduce condensation, and using high-quality fuel additives that disperse moisture. If contamination occurs, immediate removal and filter replacement can protect your engine and keep your diesel running at peak performance.
Diesel fuel is the lifeblood of diesel engines everywhere—from heavy trucks to military vehicles operating across harsh environments. But water contamination can wreak havoc on your fuel system, leading to issues like corrosion, poor performance, and even engine damage. Understanding how water gets into diesel and how to remove it is essential for anyone who depends on reliable diesel power.
Water can enter a fuel tank in several ways. Condensation from temperature changes is one of the most common causes. As air moves in and out of the tank, moisture forms on the inside and eventually mixes with the diesel fuel. This is especially likely when tanks are not kept full—more empty space means more room for condensation to form.
Rainwater and contaminated transport or storage systems can also introduce water into diesel fuel. Once water enters the gas tank or storage tank, it can settle at the bottom since water is heavier than diesel fuel. In colder climates, water may freeze and block fuel lines, creating significant operational problems.
Over time, water in the tank allows microbes to thrive. Bacteria and fungi feed on fuel oil, producing slime and acids that accelerate corrosion and clog filters. This microbial growth is a leading contributor to clogged filters and fuel system issues.
Water in the gas or diesel can cause a range of symptoms and performance issues:
Hard starting and rough idle
Reduced fuel efficiency
Loss of power and poor acceleration
Corrosion of fuel system components like pumps and injectors
Increased maintenance costs over time
Water doesn’t burn like diesel fuel; instead, it interferes with combustion and can damage key components such as fuel injectors and the fuel pump. In extreme cases, contaminated fuel can cause complete engine shutdowns.
Thankfully, there are effective ways to remove water and protect your diesel fuel system:
1. Water Separators and Filtration Systems
Diesel fuel filtration systems that include water separators are essential. These devices pull water out of the fuel before it reaches critical components, helping prevent damage and maintain performance.
2. Draining the Tank Regularly
If water has collected at the bottom of your fuel tank, it may be necessary to drain and clean the tank. This removes accumulated water and any microbial slime that has developed.
3. Fuel Additives
Quality fuel additives can help disperse small amounts of water so that it gets burned off during combustion or more easily removed by your filtration system. These additives can also help control microbial growth and improve fuel stability.
4. Maintain Full Tanks During Storage
Keeping tanks as full as possible minimizes the air space in the tank. Less air means less condensation and less opportunity for water to form and enter the diesel fuel.
Signs of Air in Your Diesel Fuel and Airlock Symptoms
Learn how AirDog fuel systems solve air intrusion problems in our article on AirDog® Superior Standards for Diesel Fuel Systems
