How to Seal a Plastic Gas Tank

Co-authored by Eric McClure

Last Updated: February 5, 2020 References Approved

Plastic gas tanks are in high demand in the world of motorcycle racing and ATV enthusiasts. A plastic gas tank can weigh less than half of a comparable metal gas tank and it is easy to mold into shapes to fit odd configurations. Seamless gas tanks seldom leak and are impervious to the rust and corrosion that affect metal tanks. If a plastic fuel tank does sustain small holes or tears, there are several fairly easy ways to make the repair.

Method 1

Method 1 of 3:
Seal Plastic Gas Tank with Epoxy Glue

1
Drain the gasoline from the tank and allow it to dry. Sand the area around the hole or crack, and clean the area with a shop cloth saturated with rubbing alcohol.^{[1]
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2
Mix the 2 part epoxy together and apply all around the perimeter of the opening.^{[2]
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Research source} Cut a fiberglass patch large enough to cover the opening and overlap it.
3
Place the fiberglass patch over the hole and press into the epoxy. Apply more epoxy to the patch and surrounding area, pressing firmly to saturate the patch.
4
Allow to dry, sand the patched area smooth and spray paint with a plastic paint if desired.

Method 2

Method 2 of 3:
Seal Plastic Gas Tank with a Plastic Welder

1
Buy or rent a plastic welder. Tell the salesperson what you are doing with it to ensure that you get the correct rods.
2
Remove the plastic gas tank from the vehicle, and set it up in a secure welding area. Drain the gasoline from the tank, and allow it to dry both inside and outside. Don protective eye gear, a welding helmet and welding gloves.
3
Use a plastic welding rod made specially for this purpose, and fill in the crack or hole. Start at an edge and run the bead completely around the opening. Then begin crossing over the hole, allowing the rod to fill in the hole completely.^{[3]
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4
Allow the weld to set up, sand it smooth and, if desired, paint it with plastic spray paint.
5
Replace the repaired plastic fuel tank on the vehicle.

Method 3

Method 3 of 3:
Seal Plastic Gas Tank with a Soldering Gun

1
Drain the gas tank, and clean it inside and out with soapy water.^{[4]
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Research source} Lightly sand the perimeter of the area to be repaired.
2
Cut a plastic patch, made of a similar material to the gas tank, slightly larger than the hole to be repaired.
3
Heat up an electric soldering gun, and drag it around the edge of the crack to create a trench. Move the gun from side to side to push the plastic back into the trench. While the plastic is still soft from the soldering, lay the plastic patch over the area. Continue moving the soldering gun over the area to smooth the plastic, and fuse them together.^{[5]
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4
Allow to cool and dry completely. Mix a 2 part epoxy glue, and cover the entire area of the patch.^{[6]
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Research source} Allow to set up, sand and spray on a coat of plastic paint if desired.

Community Q&A

Question

Is Flex Seal gasoline resistant?

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Staff Answer
This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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Staff Answer

According to the manufacturer’s website, Flex Seal is not a good choice for sealing gasoline tanks. It’s not made to withstand a lot of heat or pressure, and it’s not recommended for use with flammable liquids, such as gasoline.
Question

How do you fix a plastic gas tank on a lawnmower?

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Staff Answer
This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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Staff Answer

A fiberglass repair patch will work well for this job. Drain the tank and let it dry completely first, and don’t forget to sand the area around the leak or hole so that the adhesive compound can adhere properly.
Question

Will Teflon tape seal in gasoline?

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This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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No, the gasoline will eventually break down the tape. If you want a quick and easy fix, a fiberglass patch is a better option.
Question

Can I use JB Weld on a gas tank?

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Staff Answer
This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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Staff Answer

J-B Weld can be used for a temporary wet repair to a gas tank. Follow the manufacturer’s instructions and be sure to treat this as a temporary fix before replacing your gas tank, as it’s only a short-term patch-up solution.
Question

Is J-B plastic weld gas resistant?

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This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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According to the manufacturer’s website, "When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical."
Question

What type of plastic is used in fuel tanks?

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The main type of plastic used in fuel tanks is high-density polyethylene (HDPE), and this shaped by a process known as "blow molding" (Wikipedia). Other plastics that may be present in fuel tanks include: Polypropylene (PP), regrind plastic (recycled polyethylene) and possibly plastic adhesives.
Question

How do you fix a leak in a gas tank?

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This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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It is recommended that you follow the steps above, which explain how to seal small holes and tears. If the hole or tear is large, it is likely beyond repair and will need to be replaced.
Question

Can a seam in a lawnmower's plastic fuel tank be repaired using a hot glue gun?

Community Answer

Probably not. The best way to repair is a plastic welder with a plastic rod that matches the plastic of the tank.
Question

Can I seal a plastic gas tank with fiber glass?

Community Answer

Yes. Use a product called Tiger Paste, which is fiberglass and resin all in one. The tank MUST be clean of all dirt, grease and oil. Seal the entire tank except for filler and any vent pipes, or pick up tube openings.
Question

What grit of sandpaper should I use to sand a plastic fuel tank?

Community Answer

You should use 80 or 100 grit sandpaper. 60 grit will work, as well. The idea is to scuff the area, so that the epoxy will have a stronger bond.

Warnings

A plastic welder is safe around gasoline and gasoline fumes, as it has a very high flash point. However, use common sense and do not use near open flames.

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