Is it Bad to Leave Gas in Lawnmower Over Winter?

It is harmful to your mower to leave gas in it over winter. Fuel left in your mower may expire and damage your lawn equipment over time. Instead, you should siphon out excess gas or add a fuel stabilizer before storing your mower for the season.

This article dives into why you shouldn’t leave gas in your mower over winter and what can happen if you do. It also explains the best ways to winterize your fuel to keep your equipment working longer. 

Why Shouldn’t I Leave Gas In My Mower?

Leaving gasoline in your mower can damage it significantly over time. And in the worst-case scenarios, it may leave your mower completely inoperable come spring.

Furthermore, gas expires. Fuel left in your equipment will become less potent or useless over the course of months or years. Not to mention it’s a waste of your hard-earned money.

What Happens If I Leave Gas Over Winter?

Leaving gas in a mower over winter causes various issues. Here are some of the most common ones:

  • Moisture from gas that’s been sitting for months causes internal rusting/corrosion.
  • Your equipment might not be able to start if the fuel is too expired.
  • Mowers with old gasoline might stutter or perform poorly.

In addition, these problems may combine and leave your machine essentially broken (or in need of expensive repairs).

How Long Until Gas Expires Inside a Mower?

According to J.D. Power, ethanol gasoline without preservatives starts degrading after about 30-90 days. Regular fuel lasts a little longer at 3-6 months. However, this varies depending on environmental conditions.

This is important to keep in mind because winters are different lengths in different regions. So, it’s less problematic for some people to leave fuel in their mowers over winter than for others.

What Happens When Gas Expires?

After expiration, your mower fuel will slowly begin to lose its potency. 

That’s not too bad on its own. But if enough time passes, it may become more viscous and gunky. And ethanol fuel may bring more moisture from the air into your engine. 

These issues can hamper your mower’s performance. So, you generally don’t want to leave gas there too long.

What Should I Do To Winterize My Mower?

Instead of leaving gas in your mower, you should siphon it out before long-term storage. 

Alternatively, you can use fuel stabilizing additives to extend your gas’s life and reduce the damage it causes.

Next, let’s examine these options and how you can utilize them to winterize your lawn equipment.

How Do You Siphon Gas Out?

Siphoning gas will take it out of your mower, so it doesn’t sit there over the winter months. Many recommend the standard sucking method.

But I will share a secret way of doing it that doesn’t involve almost drinking gas. Unless you like the flavor, of course.

  1. Open both your mower gas tank and a separate canister.
  2. Connect the two openings with a siphoning tube. Make sure it’s pretty deep in so it won’t flail out.
  3. Put a second tube into the mower gas tank, and cover any opening left with your hand or a rag.
  4. Blow into the second tube until you see fuel in the first tube. Then, stop blowing.
  5. Keep the first tub steady as it siphons gas into your canister.
  6. Run your mower afterward to get rid of any excess fuel.

Voila! That’s how you siphon gas.

Can Siphoning Gas Out Cause Problems?

While removing gas solves plenty of issues, it causes others. In fact, some experts believe that siphoning fuel out of our tank can be just as bad as leaving it over winter.

Draining all the gas in your mower leaves its components exposed to air. That can accelerate oxidation (rust) through water vapors.

Furthermore, any fuel left behind may still expire and harden in random spots. This muck can block certain valves and lead to engine issues.

Not to mention your mower may have trouble starting in the spring if it’s dried out too much. In that event, you may require fuel additives or need to warm up your mower in the sun.

What Are Fuel Stabilizers?

Fuel stabilizers are probably the best way to winterize your mowers in terms of fuel storage. 

These additives mix with your fuel to prevent evaporation and maintain combustive potency. This doesn’t just mean your gas lasts significantly longer; it also mitigates some of the damage that gas would usually cause if left in a mower over winter.

How Do You Use Fuel Stabilizers?

Using a fuel stabilizer is pretty straightforward:

  1. Consider getting fresh fuel for your mower. The stabilizer will maintain the potency of old fuel, not reinvigorate it.
  2. Add the fuel stabilizer to your mower’s gas tank (or your canister if you put your gas there).
  3. Run your machine for a few minutes afterward to get the stabilizer in your mower’s valves and lines.
  4. Check how long your stabilizer lasts and reuse it accordingly.

By taking the time to winterize your mower properly with a stabilizer, you’re increasing its efficiency and extending its life.

Help! What If I Already Left Old Gas In My Mower?

If you already left gas in your mower over winter, don’t panic! 

While old fuel may cause problems, modern mowers are pretty hardy. So, you might be OK. Just don’t make it a habit if you want to keep your lawn equipment in top condition for longer.

Also, don’t just add a fuel stabilizer if winter is already almost over to “refresh” your fuel. It won’t do anything to make old gas more potent. 

Instead, just try running the expired gas out of your mower. If your mower struggles to start, consider siphoning the old gas out.

What If I Have A Riding Mower?

Winterizing your riding/tractor mower is mostly the same process as preparing your push mower. You want to siphon or stabilize the fuel.

However, there’s one additional step for you to consider.

For riding mowers, you should carefully remove their battery over the cold months. This is because extreme temperatures can reduce the effectiveness of these batteries over time. 

So, you’re better off storing it somewhere cool and dry inside.