Why is My Lawn Mower Gas Cap Leaking?

You’re halfway through your lawnmowing session when you suddenly smell a gasoline smell around the tank and drips of gas leaking from the cap! Just the smell around the tank alone will indicate that your mower’s gas cap is leaking, and you’ll need to shut that off immediately.

If left unattended and untreated, it ends up being dangerous for the rider, the gas, and the mower itself. You wouldn’t want your lawnmower to consume even more gas than it should, which is costly. So you’re probably wondering, why is my lawnmower gas cap leaking?

Read on to find out the possible reasons why!

lawn mower gas cap leaking

Why Is My Lawn Mower Gas Cap Leaking?

The gas cap on a fuel tank is a crucial role in the mower’s evaporative emission system. It is a reliable seal, preventing any dust and debris from coming into the gas tank and keeping anything from spilling. But over time, as you refuel your mower, the gas cap would wear out.

You will know if you have a bad gas cap if you notice the following:

1. Fuel Smell

This is a common and major symptom of a broken gas cap. It would leak a fuel smell around your lawnmower. A broken gas cap would allow fuel vapor from the gas tank to start leaking from a filler neck.

If you notice this as you mow your lawn, switch off your mower immediately and take it to storage, away from flammables, to repair immediately.

2. Cap Doesn’t Tighten

Another common sign of a broken gas cap is if the cap itself won’t tighten well. The gas cap would click when it seals air with the filler neck. If ever you don’t hear a click or see it become loose even after the click, then it means it is leaking fuel vapor.

3. Fuel Cap Venting Test

Another way to find out if you have a broken gas cap is to conduct a short fuel cap venting test. This will show if your fuel cap works well or if it isn’t venting well.

Do this by unleashing your fuel wire, using a container to reserve fuel until your fuel tank is completely empty. Afterward, check if your mower’s tank is empty or not.

If it is, then the fuel flow would gradually become slower. If ever there is fuel left in the tank, then your gas cap isn’t venting properly and you’ll need to repair it.

Problems Behind the Gas Leak

If ever you notice your mower leaking gas, here are the common problems to watch out for:

1. Worn Out Gasket

If you notice a gas smell around the lawnmower, it may be leaking from the carburetor, which also means your carburetor bowl gasket is worn out.

2. Broken Float Assembly

The gas cap has a lot of float assemblies operating. Any defects in the float assembly would cause problems, including gas leaks. Float needles, float valves, or even the float itself may end up becoming defective because of the leaking gas.

3. Leaking Fuel Line

While this isn’t directly related to the problem as to why your lawnmower gas cap is leaking, the consequences are similar and need to be addressed.

4. Brittle Primer Bulb

The primer bulb is what will draw fuel from the mower’s carburetor when pushed for priming the engine as you start for the first time. Over time, the rubber bulb ends up getting cracked or brittle, causing the bulbs and gas cap to start leaking gas.

5. Other Issues

There are also other issues to take note of, such as:

  • You overfilled the tank with too much gas
  • Your vents are dirty and need cleaning
  • Loose bolts or mounts
  • Unbalanced blades
  • Bent crankshaft
  • Broken parts

Now that you know why your gas cap leaks, what is the solution? Here are a few tips you can follow:

  • Replace the whole gas cap using the original factory parts, which is the instant solution. Just make sure you’re careful when replacing it to prevent extra force, which spoils your air seal.
  • Insert a new rubber gasket, which will help make sure that your filler neck has an air-tight seal, preventing any dust and debris from entering the fuel tank while maintaining good venting.
  • Use a ziplock bag as a temporary solution until you can have it repaired and replaced. Doing this holds gas in the bag and you shouldn’t use it while mowing the lawn.
  • Have it checked by a professional to make sure there aren’t any broken parts in the mower.

Wrapping It Up

After all of what was said above, you might be asking if you can use a mower without fuel caps as a quick solution. While Internet users have said it works, this is NOT recommended at all, as gas would spill as you use the mower. This isn’t only a fire hazard, but unhealthy for your grass and any nearby plants, so have your gas cap fixed right away.

I hope that you learned a lot about why your lawnmower gas cap is leaking and what to do about it. If ever your lawnmower seems to have a leaking gas cap, it’s time to have it fixed right away after identifying the issue. Good luck!

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