Water in Fuel: How to Spot Problematic Contaminated Diesel Fuel Symptoms

Mon, Nov 30, 2020

The topic of fuel contamination, especially water contamination in diesel fuel, is an issue that’s not going away. If you store diesel, you’ve probably wondered what happens if water gets in your diesel fuel tank. Here we explain the symptoms of water contamination so you know when to act!

How does water get in your diesel fuel tank?

Water in fuel is a common issue caused by rainwater getting into your diesel tank through an open fill point or vent or condensation. The air in the fuel tank expands in warm conditions and is forced out of the tank vent, but when temperatures go down the cold air is sucked in which creates water droplets on the tank walls.

Whilst all fuel can suffer from water contamination, the increasing bio-content in today’s diesel means that these water levels are more problematic than ever before. Biodiesel naturally contains some water content. This, combined with the fact that it is hygroscopic, meaning it attracts and holds onto water, makes it an even more likely victim of such contamination.

So, what are the symptoms of contaminated diesel fuel?

If you store diesel fuel on-site and suspect you have water contamination, you can have your fuel tested or can use water finding paste to detect water sitting at the bottom. However, as a tank owner, it is important to be able to spot contaminated diesel fuel symptoms yourself. Do you know what to look for?

Bound (suspended) water vs free water

The appearance of your fuel

Diesel usually appears clear and bright, but when the water content exceeds that which the fuel can handle, this can change. What you may not know is that water contamination in diesel fuel can appear differently!

  • Free water – As its name suggests, free water is present within the tank but exists completely separate to the fuel. It sinks to the bottom of the tank, creating a layer of water under the fuel. It is here that diesel bug often grows which puts your equipment, vehicles and engines at risk.
  • Suspended water – Now, it is this type of water contamination that is responsible for your cloudy diesel fuel. Suspended water is that which is bound to the fuel molecules and is essentially mixed in with the fuel making it appear cloudy. As the diesel becomes so full of water that it can hold no more it starts dropping free water out to the bottom of the tank.
  • Emulsified water - Under pressure changes, agitation and heavy cavitation, often experienced as the fuel passes through pumps and filters, the water content can become completely emulsified turning it from cloudy to milky diesel fuel. This is where there is almost no separation between the fuel molecules and water content.

Regularly replacing filters

The first contaminated diesel fuel symptoms that you are likely to notice when contamination becomes an issue is your fuel filters getting full more quickly than normal. Since the filters are designed to catch and hold water, if you have a large problem with water in your fuel, you will end up replacing your filters more often. The other cause of blocked filters could be the presence of nasty sludge.

The appearance of sludge or “diesel bug”

Foot valve

A nasty brown or black sludge is a key indicator that water contamination in your diesel fuel has got to the next stage in causing a problem for you. The area between the fuel and water is the perfect environment for the growth of bacteria known as “diesel bug”. Over time the bacteria grow and feed creating colonies that become very difficult to break up, resulting in the sludge. So, when changing your filter, don’t forget to check for traces of sludge and find if you have a problem with water contamination.

Tank corrosion

The final contaminated diesel fuel symptom is rust and tank corrosion which usually indicates a serious problem. If contamination is not dealt with and left to worsen, diesel bug will eventually start to eat away at the tank. Check your tank for rust, cracks and holes.

Rusty fuel tank

What happens if water gets in the diesel fuel tank?

If water is left untreated in your tank, there are several costly problems that you can encounter.

Blocked filters and damaged pumps

The nasty sludge the diesel bugs produce can end up blocking filters and damaging your pumping system. Not only can this result in extremely costly repairs and excessive spend on filters, but it can also result in you not being able to dispense your fuel and therefore downtime in being able to use your machinery or equipment.

Engine issues

Once the contaminated fuel gets into your vehicle, you may start experiencing issues such as power loss, spluttering and involuntary speed changes. These are signs that the fuel isn’t burning as it should do because of the water, or perhaps because the sludge is restricting fuel flow to the engine.

Corrosion of the fuel system

This may occur as water contamination in diesel fuel become more serious, and water corrodes engine components. The reduced lubricity can also cause premature wear and damage injectors. This problem is difficult to be detected in the early stages as it develops over time, so you need to act early.

Fuel inefficiency

You may also notice your fuel economy is reduced and are getting less miles/output per gallon. This is because the water in fuel reduces the CETANE level of fuel, which can prevent the fuel from burning as it should.

If you are concerned about contaminated diesel fuel symptoms, you need to take action as soon as possible to prevent serious issues and costly downtime. Water in fuel is an issue in the fuel industry that is not going away, so you need to be considering the options to prevent water contamination from becoming a serious problem such as how to remove water from fuel tanks.

See how to prevent water contamination...

Read how to deal directly with these problems and the importance of removing both the free and emulsified water.