Contaminated fuel: The symptoms to watch for (and how to avoid it)

Five minutes after pulling out from the servo, you notice your car doesn’t sound quite right. It’s down on power, maybe a bit rough, and then – bang – a warning light pops up on the dash. That sinking feeling? It could be contaminated fuel.

It doesn’t happen often, but when it does, it can get expensive very quickly. We’re talking thousands of dollars in damage if things go really pear-shaped. So, in this article, we’re going to look at what fuel contamination is, how to prevent it, and what to do if it happens to you.

Contaminated fuel symptoms: what to look for

If you’ve picked up bad fuel, the signs usually show up pretty quickly – often within 5-20km of leaving the pump. You’ll notice signs such as:

• Engine running rough or misfiring
• Noticeable loss of power
• Difficulty starting
• Engine warning light on the dash
• Unusual noises from the engine

If you experience any of the above shortly after filling up, don’t keep driving. The longer contaminated fuel circulates through your system, the more damage it can cause.

What is fuel contamination?

Your engine is designed to run on a precise mix of fuel and air. No matter how small, anything else in that system can throw things out.

Fuel contamination generally falls into two categories: solid contaminants and foreign fluids.

Solid contaminants

Solid contaminants are tiny particles of things (the gritty stuff) like:

• Rust flakes
• Dust and dirt
• Debris from storage tanks

These particles can clog injectors and damage components over time.

Foreign fluids

Foreign fluid (the big problem) is typically water, which is as good for an engine as ingesting petrol is for you. It can cause corrosion, reduce lubrication, and, in diesel engines, lead to bacterial growth (diesel bug) that clogs the system.

Why it happens (and why it’s worse in the bush)

Fuel contamination is relatively rare, but it does happen.

According to the RACV, there were around 1,300+ cases over two years. Not huge numbers, but enough to be a real risk, especially if you travel regionally.

You’re more likely to encounter contaminated fuel in rural areas because regional servos do not cycle through their fuel as quickly, giving time for contamination such as condensation to form, leading to water ingress and even ‘diesel bug’, a bacteria that enjoys growing at the junction of diesel and a tiny amount of water. Regional storage systems may be older and less maintained.

Modern engines – especially diesels – are also far less forgiving than older setups. High-pressure systems and tight tolerances mean even small contamination can cause big issues.

What to do if you suspect contaminated fuel

If your vehicle starts playing up shortly after refuelling:

Stop driving immediately

If you suspect fuel contamination, stop immediately, as continuing to drive can spread contaminated fuel throughout the system. Many contaminants, water included, sink to the bottom of the tank where the pickup is, so waiting for everything to settle, then draining a couple of litres may help.

In some cases, mechanics may be able to drain the tank and minimise damage, but timing is everything.

Contact the servo

Let them know what’s happened. If others report the same issue, it strengthens your case.

Keep your receipt

This is critical if you need to claim compensation.

Check your insurance

Your insurance may cover you for fuel contamination.

Report it if needed

You can also report the incident to the Department of Climate Change, Energy, the Environment and Water and also to your state’s Fair Trading and Consumer Affairs agency.

How to reduce the risk of contaminated fuel

You can’t eliminate the risk entirely, but you can stack the odds in your favour by doing the following:

Avoid filling up on empty

In some cases, contaminated fuel can be diluted. For example, if you accidentally put a litre of petrol into a diesel tank that’s three-quarters full, you’ll probably not do any damage. But put 70 litres of contaminated fuel into a diesel tank that’s on the red needle, and you’ll need to call a misfuelling service quick smart.

This is where a long-range tank can be handy; just keep on topping it up, right? However, this method doesn’t offer complete protection, as fuel is drawn from the bottom of the tank, which is exactly where water and many other contaminants will sink.

Don’t be first at the pump

Bad fuel can either be delivered, or it can go bad when it is stored. If you’re the first car through after the tanker has visited, that increases your risk.

Be selective about where you fill up

A run-down servo with low turnover? Probably worth skipping.

Be cautious after floods

Water ingress into underground tanks is a real risk after flooding events.

Do a visual check (if you’re keen)

Light aircraft pilots learn to drain a sample of fuel from each tank and visually check it for colour, water and presence of matter. This is not a foolproof method, as an inspection may not catch all bad fuel, but sometimes you will be able to see problems.

To check, decant a glassful of fuel into a transparent container and inspect. You’ll need to be familiar with what good fuel looks like first though, so practice at home with some fuel, water and fine dirt.

Prevention: is extra filtration worth it?

Your vehicle already has a factory fuel filter, typically capable of filtering particles down to around 2-5 microns. So why not just add another ultra-fine filter? Because modern vehicles monitor fuel pressure. Adding overly restrictive filtration can trigger warnings or affect performance.

What about water in fuel?

This is where things get serious. Water is one of the most damaging forms of contamination, and it’s also one of the hardest to deal with once it reaches your engine. Some vehicles come with a built-in water trap, but many owners choose to add an extra layer of protection.

A water/fuel separator, like those available from Ryco, is designed to remove water before it gets into your engine. These systems allow water to settle and be separated from the fuel, helping reduce the risk of corrosion, injector damage and costly repairs.

We love the Ryco one below as you don’t need to do a visual inspection of the bowl and draining when full. It comes with a Sensor Kit that allows you to log into the Ryco Connect App or you can let the Ryco Bluetooth Sensor Indicator let you know when it’s time to drain the unit.

Low risk, high consequence

Fuel contamination isn’t something most people will deal with regularly. But when it does happen, it can mean replacing injectors, cleaning or replacing fuel lines and damage to pumps and tanks. You’d be lucky to walk away with a $5,000 bill. $10,000 isn’t unheard of.

Fuel contamination sits in that annoying category of “unlikely but expensive”. You don’t need to lose sleep over it, but it’s worth knowing the signs, taking a few simple precautions, and understanding what your options are if things go wrong.

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