Water in the Fuel Tank: Symptoms, Causes and How to Treat It

Water in the fuel tank is one of the most searched car problems on Google: how do I know if there is water in my petrol or diesel?, why does my car stall or jerk after refuelling?, what should I do if water has been put in my tank? In this guide we answer, one by one, the questions drivers ask most, and explain what the data sheet of NF Fuel Guard says, the NF Booster Europe additive specially formulated to address problems caused by water contamination in fuel.

What happens if there is water in a petrol or diesel tank?

Water does not mix well with fuel: it is denser and tends to settle at the bottom of the tank, which is exactly where the fuel pump draws from. As a general rule, this can cause poor running, jerking, hard starting and even stalling. In diesel engines, water can also encourage corrosion and the growth of algae and microorganisms in the fuel (the well-known Fuel Bug).

How do I know if there is water in my fuel tank? Most common symptoms

As a general rule, these are the symptoms usually linked to water in fuel. None of them is conclusive on its own, so if in doubt, have the car checked at a workshop:

• The car stalls suddenly, especially shortly after refuelling.
• Jerking, hesitation or loss of power when accelerating.
• The engine runs roughly or idles unevenly.
• Hard starting or no start at all.
• Abnormal exhaust smoke.
• Water-in-fuel-filter warning light on, in diesels that have one.

Why does my car stall or jerk after refuelling?

If the car stalls, won't start or jerks right after refuelling, one possible cause is water in the fuel. It could also be a clogged filter, an injection problem or an electrical fault, so it cannot be confirmed without inspecting the vehicle. If it happens to you, it is wise not to keep cranking the engine and to talk to a workshop.

Why does water get into the fuel tank? Most common causes

Water can reach the fuel in several ways. The most common causes are:

• Condensation: humid air inside the tank condenses on the walls, especially with temperature changes.
• A nearly empty tank for a long time: the more air inside, the more moisture can condense.
• Fuel stored for a long time: cars, motorcycles or machinery left unused for months.
• Refuelling with contaminated fuel: for example, a pump whose underground tank contains water.
• A loose or damaged fuel cap, letting rain or moisture in.
• Floods or very heavy rain.

Water has been put in my tank: what should I do?

As a general recommendation: do not start the engine if you suspect you have refuelled with water-contaminated fuel, or if a significant amount of water has gone in. If it is already running, stop in a safe place and switch it off. The usual solution is to have the tank and lines drained and cleaned at a workshop. If the contamination is slight, there are additives designed for that purpose, such as the one described below.

Can I start the car with water in the tank?

It depends on the amount and on whether the water has already reached the injection system. With a significant amount, it is wise not to start it, because the engine, and especially a diesel injection system, can be damaged. With slight contamination from condensation the vehicle may keep running, although it is advisable to treat the fuel. If in doubt, ask a workshop.

How do you remove water from a fuel tank?

There are two main routes. The first is to drain and clean the tank at a workshop, which is the answer when there is a lot of water. The second, for slight contamination such as condensation, is to treat the fuel with an additive specific to water, such as NF Fuel Guard, so the tank does not need to be drained.

NF Fuel Guard: what its data sheet says

NF Fuel Guard is a highly concentrated product, specially formulated to address problems caused by water contamination in fuel. According to its data sheet:

• It dissolves water and condensation in fuel tanks, and the water ends up evaporating through the exhaust.
• It revitalises aged fuel.
• It removes varnishes, gums and acids from fuel tanks.
• It prevents and eliminates Fuel Bug and algae.
• It treats up to 1,200 litres of petrol or diesel (300 litres in extreme cases).
• It is safe for catalytic converters and oxygen sensors, and non-flammable.
• It can be used in both vehicle fuel tanks and bulk storage tanks.

For the exact amount to add and how to use it, check the label on the bottle. You can see the full data sheet, with the up-to-date price, on the NF Fuel Guard page, within the additives category of NF Booster Europe.

How can I prevent water in the fuel tank?

As general preventive measures:

• Try not to leave the tank nearly empty for long periods.
• Check that the fuel cap closes properly and is in good condition.
• Avoid refuelling at stations with roadworks, puddles around the tank covers or a poor reputation.
• If the vehicle will be unused for a long time, bear in mind that stored fuel can age and collect moisture.
• Have the fuel filters checked according to your vehicle's maintenance schedule.

Frequently asked questions about water in the fuel tank

How do I know if there is water in my petrol?

Typical symptoms are stalling, jerking, hard starting or rough running. As they can be caused by other faults, the most reliable way is a diagnosis at a workshop.

What happens if I put petrol with water in my car?

As a general rule, water can cause jerking, loss of power, hard starting or stalling. With a significant amount, it is wise not to start the engine and to go to a workshop.

What happens if there is water in diesel?

In a diesel, water can affect the injection system and encourage corrosion and the growth of algae (Fuel Bug). If you notice symptoms or suspect it, have it checked as soon as possible.

Why did my car stall after refuelling?

One possible cause is fuel contaminated with water, although it could also be filters, injection or electrics. If it happens, it is better not to keep cranking the engine and to talk to a workshop.

Can condensation put water in the tank?

Yes. Humid air inside the tank can condense, especially with temperature changes and when the tank is low for a long time.

Is there an additive to remove water from the tank?

Yes. According to its data sheet, NF Fuel Guard dissolves water and condensation in fuel tanks, and the water ends up evaporating through the exhaust.

Does NF Fuel Guard work with petrol and diesel?

Yes, it treats up to 1,200 litres of petrol or diesel (300 litres in extreme cases).

Is NF Fuel Guard safe for the catalytic converter?

According to its data sheet, it is safe for catalytic converters and oxygen sensors, and non-flammable.

What is Fuel Bug?

It is the name given to the algae and microorganisms that can grow in fuel when water is present. According to its data sheet, NF Fuel Guard prevents and eliminates Fuel Bug and algae.

Does it work if the tank is full of water?

That is not what it is for. If the tank contains a significant amount of water, the right move is to have it drained and cleaned at a workshop. The additive is designed to treat fuel contaminated with water, not to replace that draining.