Its all about the Science! Written specifically for the NAACC Membership and Friends.

Hopefully, when you put your vehicle or boat up for the winter, you followed the proper winterizing steps to minimize what you have to do to get it ready for summer rec use. If your car has been sitting since last season with untreated gasoline in the tank, there’s a good chance it isn’t. And if that gas contains ethanol—as most gas pump fuel does—you’re facing an even higher risk of performance problems that can put a real damper on the smooth touring you’re hoping to enjoy this season.

What Happens to AUTOMOTIVE  Gasoline During Storage?

Gasoline—especially ethanol-blended fuel like E10 or E15—doesn’t age well. If we were talking about diesel fuel, we’d be talking about unstable cracked molecules from the refinery and how those shorten the fuel’s usable storage life. For gasoline, especially marine gas and automotive fuel, it has to do with water issues that are exacerbated by the ethanol it often contains.

The ethanol in gasoline is hygroscopic, meaning it naturally draws moisture from the air. Even in sealed systems, small amounts of air exchange and condensation can introduce water into the fuel over time.

As that moisture accumulates, it dissolves into the ethanol portion of the fuel. But ethanol has a limit to how much water it can absorb. Once that limit is reached—often after weeks or months of storage, especially in humid conditions—the fuel begins to separate.

This process, known as phase separation, doesn’t happen all at once. It occurs gradually, with the ethanol and absorbed water slowly separating from the gasoline and settling to the bottom of the tank. What’s left is a layered system: a low-octane, water-laden ethanol mixture at the bottom and gasoline floating above it.

If your engine pulls from that lower layer, it can struggle to start, misfire under load, or shut down entirely. Even before full separation, the shifting chemical balance in the tank can reduce combustion quality and lead to hard-to-diagnose performance issues. In some cases the fuel tank will also start to rust and over time may actually develop pin holes and begin to leak.

And phase separation isn’t the only threat—oxidation begins within 60 days of storage, forming gums and varnish that can clog fuel lines, injectors, or carburetors. The result: poor reliability just when you’re ready to enjoy a day on the water.

Thinking back, if you didn’t use a fuel stabilizer before storing your car, there’s a strong chance that phase separation has already occurred, especially in humid or coastal environments. When your engine draws from this layer, it can misfire, stall, or fail to start entirely. And even if it runs, you may notice hesitation or poor performance as the engine struggles to burn the diluted mix.

Even if phase separation hasn’t fully set in, fuel that sits more than 30–60 days begins to oxidize, forming gums and varnish that can clog carburetors, injectors, and fuel lines. The result? A frustrating start to your touring season, and potential engine damage if left untreated.

Common Signs of Fuel Gone Bad

Novice car collectors often blame spark plugs, filters, or electrical issues when the real culprit is untreated fuel. Keep an eye on how your vehicle first performs when you bring it out of hibernation. Some early-season red flags include:

• Hard starts or rough idling
• Engine hesitation when accelerating
• Misfires or reduced power
• Gummed-up fuel lines or filters

These problems stem from problems that developed in the elements of the fuel system. So, a good recommendation to smooth these out is using a high-detergency marine or automotive fuel treatment with enough detergency power to clean injectors and fuel lines. Assuming, of course, that you did what you were supposed to and changed your fuel filter as well. These kinds of issues are preventable—and often completely avoidable with the right fuel treatment.

How Marine Fuel Treatments Protect Your Boat AND Automobile

High-quality marine fuel treatments like Ethanol Defense and Marine Mix-I-Go are designed specifically for marine gasoline that contains ethanol. They work by:

• Preventing phase separation by controlling moisture
• Stabilizing ethanol gasoline for long-term storage (up to 12 months)
• Cleaning injectors and fuel system components, cleaning up whatever might have developed during winter storage
• Protecting metal parts from corrosion and ethanol-related damage

In other words, it keeps your fuel fresh and your engine running clean, so you’re ready to go when the season starts.

ETHANOL SHIELD IS SOLD AT CANADIAN TIRE. IT IS ALSO HIGHLY RECOMMENDED FOR YOUR COLLECTOR CAR AND LAWN AND GUARDIAN EQUIPMENT

Quick Pre-Season Fuel Readiness Checklist

Before you hit the road, make sure you’ve got the basics covered:

Q. Did I treat the fuel before storing my vehicle last season?
Q. If not, should I drain and replace it, or add a system cleaner before running the engine?
Q. Are my fuel lines and filters in good condition?
Q. Am I using a marine gas treatment like Ethanol Defense and Marine Mix-I-Go to protect against moisture and oxidation moving forward if I have a boat? Am I using Ethanol Shield if I am dealing with a collector car or garden equipment.

Don’t Let Bad Fuel Stop Your touring  

Most gasoline unfortunately contains ethanol. All gasoline in Canada has been mandated to have some ethanol content. If you want reliable starts, smooth power, and fewer maintenance headaches this summer, treating your marine or automobile fuel with Ethanol Defense or Marine Mix-I-Go is one of the smartest—and easiest—things you can do. If you have a collector car or motorcycle, make sure to use Ethanol Shield to prevent phase separation and hard starting as well as fuel tank and carburetor damage.