When caring for your lawn mower, one of the most important aspects to pay attention to is its gas cap. This part is essential in keeping a consistent fuel flow and avoiding spills that can be hazardous on the grass and other items like patio furniture.
Gas caps get lost often, the reason being that they are vibrated off during use. If this happens, replacing the Cap is essential to keep your lawn mower running correctly and safely.
The question then becomes, are lawn mower gas caps universal? The short answer is no. Mower gas caps are not universal. However, many different models are usually available that are compatible with a wide range of mowers.
Note- It can be confusing to determine whether a new gas cap fits your lawn mower, but thankfully, the critical factor is your engine’s model number rather than the lawn mower itself. Knowing which engine model is in your lawn mower can save you time and money when searching for compatible parts like a gas cap.
In this blog post, we’ll discuss what makes lawnmowers unique, identify the main types of gas caps available today, and provide helpful tips on ensuring your lawnmower responds optimally and saving gas due to faulty caps.
Function & Types Of Mower Gas Caps
Gas caps perform mainly three functions, which are as followings:
- Prevents gas spills
- Keeps crap out
- Vent the tank.
Two main types of gas caps are available for lawnmowers – the vented Cap and the non-vented Cap. Vented caps are designed with a one-way valve that releases pressure from the fuel tank. This is important as it prevents fuel from backing into the carburetor and fouling the engine. This gas cap is further classified by its material, such as:
- Winged Cap
- Threaded Cap
Winged Cap – The winged gas cap is generally metal and fitted to the top of the fuel tank. This type of Cap has several tiny wings designed to fit into grooves on the fuel tank, thus creating a secure and leak-proof seal. Although they are not frequently used as plastic threaded caps. These are mainly used for stationary engines, but some mowers still require these gas caps.
Plastic Threaded Cap – Threaded gas caps are plastic and feature a threaded neck that screws into the fuel tank, creating a tight, leak-proof seal. This type of gas cap often comes with an O-ring that helps to create an even stricter seal when screwed in place. They are widely used on lawnmowers and tractors.
Non-vented caps, on the other hand, don’t have this valve feature and are mainly used to prevent fuel from spilling out of the gas tank.
Does a Gas Tank Need to be Vented?
For years, tinkerers and DIY-ers alike have used whatever’s available regarding mower caps. That’s why, although a cap is just a cap, when it comes to lawnmowers, the type of Cap can be necessary for engine performance. If your gas cap isn’t vented correctly – as all mower caps need to be – you’ll run into starting problems with your engine.
I’ve seen what happens when an owner reaches for an old oil can cap that fits quite well but is a potential disaster down the line if the Cap isn’t vented. As a mechanic of over two decades, I know how to recognize this situation quickly and help keep engines running optimally by recommending the right Cap for the job.
Often, the landscaper is happy with this repair; however, the engine is not running correctly again after some time. Because the old gas cap was not designed for the specific engine model, it couldn’t ventilate properly, causing fuel build-up in the carburetor.
Punching a hole in the makeshift oil cap would fix the stalling issue. However, this creates a new problem – fuel spills. That’s why it’s essential to always use the correct Gas Cap for your particular lawn mower engine. It is harmful to both environment and a fire hazard.
MacGyver Type Gas Cap
If your covering the gas tank filler neck with plastic is the same problem MacGyver fix that some people try. But, It’s important to note that this is not an actual gas cap and can be dangerous, as it will block off airflow to the fuel tank and create excessive pressure. Additionally, it doesn’t secure the fuel tank or prevent spills.
Common Signs of a bad gas cap include:
- Decrease in engine performance
- The engine stops after thirty minutes of cutting and won’t restart
- Poor fuel economy
- The gas smell from the exhaust
- Engine stalls or stutters when idling
If you want to buy a mower cap, check out the Amazon link below.
Frequently Asked Questions
What happens if a gas tank is not vented?
With proper ventilation, pressure can build inside the tank, making it easier to fill the fuel tank. Additionally, when a gas tank isn’t vented, fuel vapors can escape, which could be hazardous if they come in contact with an ignition source.
Is there a difference between a gas cap and an oil cap?
Yes, there is a difference. Oil caps are usually made of metal and feature fins that help ensure a tight fit when twist-locked to the top of the oil tank. On the other hand, gas caps typically have a threaded neck that screws into the fuel tank creating a leak-proof seal. They also usually come with an O-ring that helps to create an even tighter seal when screwed in place.
Does fuel need air?
Yes, fuel needs air to combust. Without oxygen in the combustion process, the power will not be able to burn and create energy for the mower engine. This is why it’s essential to use a vented gas cap so that air can enter and exit the tank as needed.
Maintaining a good gas cap is essential for running your lawn mower smoothly. Gas caps help keep the fuel in your gas tank secure and provide a proper venting system for your fuel tank.
Without the correct gas cap, air can enter the fuel tank and create an emulsion that can clog up engine filters and disrupt the air-fuel ratio.
Douglas Mackalie is a Founder of Mackalies Garden. He is one of the most exciting people you’ll ever meet. He has 25 years of experience in horticulture and gardening, most of which he’s spent outdoors getting his hands dirty.