How to Fix a Plastic Gas Tank - man opening a gas tank

How to Fix a Plastic Gas Tank on Your Lawn Mower

If you’ve recently noticed a crack, split, or leak on your mower’s plastic gas tank, you’re probably wondering whether you can fix it or if you should just replace it. As long as there isn’t a gaping hole in the tank, it’s most likely repairable!

There are many different ways people try to fix a broken plastic gas tank, but if you’re looking for something permanent (rather than a temporary solution), read on to learn how to repair your plastic gas tank!

What You’ll Need

  • Soldering Iron
  • Air Compressor
  • Rubbing Alcohol
  • Cotton Swab
  • Sandpaper
  • Water
  • Dish Soap
  • Spray Bottle


1. Check for leaks

You already know there is at least one crack, but there may be others that are hard to see. To find them, fill up your spray bottle with water, then add dish soap. Shake to mix, then spray this solution on a section of your gas tank. After you’ve sprayed a section, ensure the gas cap is on tightly and slightly compress the tank.

If you see any bubbles pop up, this means there is a crack there (the air inside is being forced out, creating bubbles in the solution). For maximum accuracy, check the tank in small sections. Repeat this process until you are sure you’ve located all of the cracks.

2. Remove any fuel from the tank

After you’ve removed any gas, leave the gas cap off of the tank. Take your air compressor and blow out the inside of your gas tank until you are confident that no gasoline fumes remain. Although it’s highly unlikely that the soldering iron will cause any sparks capable of igniting the fumes, it’s always best to err on the side of caution anyway!

3. Sand down the surface around the crack

Use sandpaper on the area around the crack, making it smooth as possible. This makes the plastic easier to work with, eliminates surface dirt/grime, and also removes some of the gasoline/oil on the plastic.

4. Clean the surface around the crack

Since we’re going to be melting the tank back in on itself, we want the plastic to be as pure as possible. This means getting all gas, oil, and other contaminants off of the surface we’ll be melting. Soak your cotton swab in rubbing alcohol, then use it to clean off the crack. Make the area as clean as possible before moving onto the next step.

5. Use the soldering iron to create a groove

how to fix a plastic gas tank - soldering iron

Taking the soldering iron, push into the plastic slightly and make a groove down the center of the crack. Avoid pushing down too hard, as you don’t want to create a hole in the tank. Make sure this groove extends the entire length of the crack you’re fixing, leaving a melted groove in place of the crack.

6. Fill the groove using the surrounding plastic

Now that we’ve created a groove in your plastic gas tank, it’s time to fill it in! In a scraping motion, use the soldering iron to pull the surrounding plastic (which will be melting as you do this) into the groove. Don’t scrape too much from one spot; try to evenly scrape plastic from all around the groove to ensure the integrity of the tank.

7. Smooth out the melted plastic

Once you’ve successfully filled up the groove with the surrounding plastic you’ve scraped in there, it’s time to make it (somewhat) visually appealing. Making a circular motion, smooth out the plastic in the groove with the surrounding plastic. This will end up looking quite burnt, so don’t worry too much about getting it perfect. If you prefer a smooth surface, you can always run sandpaper over the area after you’ve smoothed it out with the soldering iron.

8. Check your work

After the plastic has re-hardened, it’s time to check your work! Fill the gas tank back up, replace the gas cap, and shake the tank. If it doesn’t leak, congratulations! You’ve successfully fixed the plastic gas tank on your lawn mower! If it does, simply repeat the process until the leak has been sealed.

Although this guide was designed with lawn mower gas tanks in mind, you can use the same process to fix the gas tanks on your weed eaters, edgers, and other handheld tools. Smaller tanks may have thinner plastic, so keep that in mind when creating your groove! 

Alternative Options

If you’d prefer to avoid melting your gas tank, you can also try a patching kit. The process is somewhat similar: start by removing any remaining fuel and sanding off the cracked area.

From here, follow the instructions on your patching kit. Some may require mixing the adhesive compound, while others may not, so make sure to read the instructions over before attempting your repair.

When Replacing Your Tank Is the Better Option

adding fuel to new tank

While repairing a tank is usually the preferred option, there are some times where repairing your tank simply isn’t practical (or feasible). Here are some situations where you’d want to consider replacing the tank altogether.

  • You have multiple holes/cracks in your gas tank.
  • The crack extends across the majority of the tank.
  • Your tank has large holes.
  • You’ve previously attempted to fix a crack, but it has returned.

Read also: How to Empty Gas from Lawn Mower

Wrapping It Up

There you have it, the 8 steps on how to fix a plastic gas tank on your lawn mower. Let me know how it goes in the comments.

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