Fuel Contamination: What You Need to Know

​Let’s face it—most of us love the freedom of being out on the water, the hum of a reliable outboard, and the simplicity of filling up and heading off. But behind the scenes, there’s one little gremlin that can turn a fun boating day into a frustrating one: fuel contamination.

Now, when people hear the term "fuel contamination," they often picture grubby fuel containers or dirt sneaking its way into the tank. While that can happen, the real culprit is often something a bit sneakier—fuel that’s simply been sitting around too long. Yep, old fuel is a silent engine killer, and it’s more common than you might think.

What Happens When Fuel Sits?
Petrol doesn’t age like fine wine. Leave it sitting for about three months, and you’ll start to lose more than just octane. Fuel starts to evaporate, and as it does, it leaves behind residue—sticky, varnish-like gunk that can clog fuel lines, filters, and injectors.

After this evaporation process, something called "phase separation" begins. This is where the ethanol in the fuel absorbs moisture from the air and separates from the petrol. Think oil and vinegar—but way worse for your engine.

This separation can cause rubber gaskets, seals, and hoses to crack, shrink, or perish completely. The result? Fuel leaks, loss of fuel pressure, poor engine performance, and in some cases, a boat that just won’t start.

But here’s the good news: all of this is totally avoidable with just a bit of simple maintenance.

How to Prevent Fuel Problems
You don’t need to be a mechanic to keep your fuel system happy. Just give your engine a little love every now and then. Here’s how:

• Start it up every two months and let it run for 10–15 minutes. This keeps the fuel moving and prevents things from settling or separating.
• If your boat has an underfloor fuel tank, go for a longer 20-minute run every eight weeks. This helps cycle fuel through the entire system.
• Using a portable tote tank? Easy. Just disconnect the fuel line and run the engine until it stops. This drains out any leftover fuel and keeps the lines clean.

It’s simple stuff, but it makes a big difference. These small actions can save you hundreds—if not thousands—in repairs, especially when it comes to outboards.

What About Water in the Fuel?
Let’s shift gears and talk about another common issue: water contamination.
Water in the fuel sounds scary, and if it's saltwater, it kind of is. But if it’s just freshwater (which is usually the case from condensation or rainwater intrusion), it’s actually not that hard to fix.
Here’s what to do:

• First, drain and clean your fuel tank. Get all the water and old fuel out of there.
• Next, flush the entire fuel system. Replace any filters and check lines and fittings.
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As long as the water hasn’t been sitting for months or mixed with saltwater, it typically won’t damage your electric fuel pumps or seals. Freshwater gets drawn into the system first, and while your engine might cough and sputter a bit, it’s usually a temporary issue.
Just be aware that water can hide in all sorts of spots—especially if your tank isn’t completely sealed—so keep an eye out for signs like rough running, stalling, or unusually high fuel consumption.

A Bit of Prevention Goes a Long Way
It’s easy to forget about the engine when the boat’s not in use, especially during the off-season. But keeping fuel fresh and the system clean is one of the best things you can do to protect your investment.

So here’s a quick checklist to wrap things up:
✅ Run your engine every 6–8 weeks.
✅ Drain fuel from tote tanks after use.
✅ Use a fuel stabilizer if storing for more than a few months.
✅ Check fuel lines and seals annually.
✅ Don’t leave tanks half full—moist air = condensation = water in your fuel.

Don't get stranded at the ramp because of bad fuel. A little regular TLC keeps things running well and ensures your time on the water stays stress-free.

Happy boating!