Written by Dale Richardson - Updated: June 23, 2023
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Today we're talking petrol lawn mowers. What are they, how do they work, what type of fuel do they need, and all of the little basics you may have missed. We scraped the web for the most commonly-asked questions related to petrol mowers and collected the answers here just for you.
So, what's on the docket today?
Today's Topics Include:
Now without further ado, let's get you some answers, yeah?
Let's start with the super simple stuff - what is a petrol lawn mower, and how does it work? If you've got more specific questions, feel free to skip on down to the relevant sections.
Now let's get going, shall we?
Perhaps unsurprisingly, breaking down how an internal combustion engine works in 300 words or less isn't really something that can be done accurately. So instead of giving you the fine details of each tiny part and how it works, we're going to break this down into a handful of sections. If you'd like to get the nitty-gritty of how and why each part of your mower works, I recommend that you check out your owner's manual or just take the thing apart! Be sure to check out our petrol mower maintenance FAQ for some of the more technical bits.
Now - how does a petrol lawn mower work?
As mentioned above, petrol lawn mowers use an internal combustion engine to power themselves. These are the same type of engine as is in your everyday car, though obviously much less powerful and quite a bit smaller in scale.
The basic way that combustion engines work is that a spark ignites the fuel (petrol) inside a specialised compartment in the engine, and the energy from that interaction is turned into power, allowing your mower to run. Generally, the blades of your engine are directly attached to the engine, which causes them to spin.
The throttle (speed of your blades) is generally controlled with a handlebar lever and affects how much fuel is delivered to the engine. This, in turn, controls how fast your blades spin.
Most traditional petrol lawn mowers use a pull cord to start the engine. You pull the cord, which gets the process of combustion started in your engine. Modern mowers often have a battery and/or starter motor that's separate from your standard motor , which makes startup drastically easier.
Your mower's blades sit at a particular height (usually around 70 mm) and can be adjusted to control how low your grass is cut. This is particularly important for properties that are hilly or have a number of rocks, as it will prevent your blades from hitting the soil or stones.
Most petrol and electric mowers change the height of the blades in different ways, but with a traditional petrol mower, you'll usually have a small lever to adjust the height of the wheels, rather than the blades. In contrast, electric mowers generally alter the height of the blades themselves.
As grass is cut, the blades rotate (much like a fan) and pull the grass up through a specialised path designed to bring all of the little bits and pieces of plant matter into a central collection bag or box. This can then be detached and emptied as needed, usually secured with a small lever.
This is one of those "yes, but actually no" types of questions. See, as I mentioned above, some modern petrol mowers do have a battery. However, the battery isn't designed to power the mower, rather, it's designed to make startup easier alongside (usually) a secondary startup motor.
In general, though, most petrol lawn mowers don't have a battery - they're generally relegated to electric mowers.
And we have yet another "yes, but actually no" question! As with all tools, lawn mowers are designed to be stored in a specific manner. That manner is in a dry, relatively warm (i.e. above freezing) environment, usually a shed or garage.
So while you can leave your petrol lawn mower outside during the summer, if done during the winter, you'll find that this can lead to a number of issues. Namely, you'll find that parts will break as things get wet, freeze, thaw, and repeat that process throughout the winter. And then there's corrosion - you'll find a number of parts (pretty much all of them) will rust over time, especially if you live in a wet and cold environment.
Those in climates like Southern California can ignore this, though it's worth noting that if you're in a very hot environment, storing a petrol lawn mower outside long-term can be dangerous. After all, heat and petrol don't mix well - in fact, you could say it's an explosive meeting...
Yes, you can store a lawn mower on its side. However, there is a caveat (shocker, I know) - some mowers are designed for vertical or horizontal storage, while others are designed to sit on their wheels 24/7.
If your mower is meant to be stored on its side or back, go bonkers. But if it's not, you will risk fuel and oil dripping into parts that you really don't want them in, like the air filters, joints, and engine.
This is one of those questions that will vary based on the type of mower you have. Commercial mowers (especially riding ones) take much more fuel than personal use ones.
The standard petrol (push) lawn mower uses roughly 1.8-3.8 litres of petrol (.5-1 gallon for the Yanks), whereas ariding mower can take upwards of 7.5 litres , depending on the tank size (duh).
While you can cut wet grass with a petrol lawn mower, it's generally not the best idea. This is for a few reasons:
The first and most simple reason to not mow a wet lawn is that wet lawns can be easy to slip on, and nobody wants to accidentally slip into an active lawn mower... yikes.
Damage to the mower:
Wet grass can leak moisture into your engine, mixing water with the fuel. That is not only a surefire way to permanently damage your engine, but a solid path to internal corrosion that can only be fixed by buying replacement parts.
Wet grass blades are harder to cut. This means that you'll be needing to go over the same spots repeatedly, see uneven cuts and even straight-up shredded bits of lawn, and just take a long time in general. Sharp blades can make this easier, but the process won't be easy , just manageable .
Plant diseases and fungi thrive in wet environments. As such, if a patch of lawn gets infected with something and you mow it, you can easily disperse that fungus or disease to the rest of your lawn. And, if bits of wet grass stick to the bottom of your mower, you can get a mouldy mower, too!
Damp lawn clippings will suffocate your lawn and cause nutrient damage to your soil. This will only get worse the longer the clippings remain in your lawn.
Cleaning up a dry lawn is as simple as dumping your lawn bag. But a wet lawn? Most of the grass won't make it into the collection bag, leaving you to rake it up while grumbling to yourself that you should've known better. And if you put it off, you get damaged and dead grass (as mentioned above).
In other words - yes you can , but you shouldn't cut wet grass with a petrol lawn mower. Check out this video if you're a visual learner like me.
Yes, petrol lawn mowers can get wet. Just be sure to dry them off when you're done to prevent rust or mould buildup.
No matter the type of engine you have in your petrol mower (2 or 4-stroke), your mower will use standard unleaded gasoline with a minimum octane rating of 87, and a maximum of 10% ethanol. Premium petrol with an octane rating of 91-93 is also acceptable.
While you can use a petrol lawn mower in the rain, I strongly advise that you practise patience, as there are more bad outcomes for mowing a wet lawn than there are good ones.
You can use e10 petrol in most traditional push mowers, but it's lower-quality petrol than is ideal. Generally, lower ethanol counts are desired, as ethanol attracts water which does not mix well with fuel. For those who are unaware, e10 fuel is petrol with 10% ethanol and 90% gasoline (the "e" stands for ethanol).
Fuel such as e5 will perform better in your engine and keep it running at a higher quality for longer.
Petrol doesn't last super long, despite the common misconception to the contrary. Generally, petrol will last for between 2-4 weeks before beginning to degrade. At the two-month mark, you'll find that the petrol will give the bare minimum in performance, and anything older than a year will work - but only barely.
The general best practise is to regularly add fuel to your mower as it's needed , and purchase more when necessary. This will ensure that your mower performs at its best possible quality for as long as possible, and will cut out some of the damage that can occur from using expired fuel.
Super unleaded fuel is acceptable for your petrol lawn mower, but it won't actively improve performance. The only type of fuel to avoid entirely for the majority of lawn mowers is diesel - that will straight-up kill your engine if you try to start it.
If you have added diesel to your petrol lawn mower's engine, do not start the engine . Pinch off or fully disconnect the fuel line, drain your fuel tank, and flush the tank and filter(s) with a new batch of regular gasoline. Then, dump your new fuel and refill the mower. Hopefully, it will start - if not, it's time for a full service or to call it a day and replace the mower.
All in all, petrol lawn mowers are complicated contraptions that make our lives so much easier when they're properly maintained. If you skip maintenance or put the wrong type of fuel in, though, you'll be in deep water quite quickly. Just be sure to familiarise yourself with the owner's manual, read carefully, and you'll be fine.
Now sit back, make yourself a drink, and maybe pop an antihistamine (my allergies are killing me just writing this piece).
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