Can You Run a Lawn Mower Without a Muffler?

You were out in the yard, minding your own business and mowing the lawn when you heard a strange noise. “Did I just run over something?” you think. No, there’s something hanging off the side of your mower. It’s the muffler. “Damn – that’s not something I can fix in 5 minutes, and I’ve GOT to get the rest of this lawn cut!”

Sound familiar? It’s happened to me before. Just before I was due away for summer vacation. I wanted to get the lawn cut to minimize the chance of returning to an overgrown yard jungle (I still did!), and my muffler went and broke. I was freaking out….could I continue or was I going to wreck my mower?

I did quite a bit of research that day. In this article, I’ll cover whether you can or can’t run a lawn mower without a muffler, what you can expect if you do, as well as any consequences of doing so.

Can You Run a Lawn Mower Without a Muffler?

Yes, you can run a lawn mower for a short period without doing any significant damage to your lawn mower. It will almost certainly run significantly louder, so it’s a good idea to wear ear protection. Running a lawn mower without a muffler shouldn’t be something that is done in the long term though, as this can cause damage to the valves in the engine.

What Will Happen If You Run Your Lawn Mower Without the Muffler?

You can probably guess by now that on the day that my muffler broke off, I did end up finishing the rest of my yard without replacing the muffler (I just didn’t have time to). Here’s what I noticed when using my mower without the muffler.

A Lot Louder

A muffler’s job is to reduce the amount of noise produced by the exhaust, as well as prevent your lawn mower backfiring. So this wasn’t really a surprise, but it was a bit louder than I had anticipated. Luckily I already own a set of ear defenders, so I used them and it wasn’t too bad at all. But you do have to think about your neighbors too, as the extra noise might bother them, especially if you mow early in the morning.

Goes Through More Gas

There wasn’t a huge difference, but I noticed that during this particular mowing session when my mower didn’t have the muffler in place, I used more gas. I suspect the engine was running less efficiently and having to work harder, hence the extra gas usage.

While I didn’t experience this myself, I expect that running your mower without the muffler could also result in backfiring, as part of the muffler’s job is to prevent that.

If I Don’t Replace the Muffler What Will Happen?

You might mow your lawn once without a muffler like I did and think “that wasn’t so bad” and delay sourcing a replacement. Let me tell you that this is a decision that could come back to bite you. I was talking to the technician in my local repair store when arranging for the installation of my new muffler, and he explained what happens when the engine is run without a muffler.

Part of the muffler’s job is to hold the heat once the engine has been shut off, and allow the engine to cool down gradually, as opposed to it going from red hot to cold in an instant. This is especially important for the engine valves, as if they cool too quickly, they are likely to bend and then need to be replaced. And that’s a whole lot more expensive than having a new muffler fitted.

When you run your mower without a muffler, especially during the cooler parts of the year, what I just described will likely happen. Cool air will get into the exhaust once you finish mowing and the temperature of the valves will drop suddenly.

Short-term savings via cutting corners normally result in long-term costs. This is no different!

A Few Tips If You Do Run a Lawn Mower Without a Muffler

If you’re in the same situation as I was, and need to run your mower without a muffler before you can get it fixed, that’s fine, but just keep the following things in mind.

• Don’t Race Around – If you’re running around your lawn like a madman, your engine has to work harder to keep up. That’s not a good idea when you’re running it without a muffler. The risk of backfiring and damage to the engine is much greater. So go at a steady pace.
• Be Careful of the Exhaust – The now exposed exhaust is going to get extremely hot. So before you even start your lawn mower up, make sure that there’s nothing in the vicinity of the exhaust, as it will burn/melt it once running. You also need to be extra careful to not go near the exhaust yourself, and make sure children or pets don’t either.
• Bag Your Clippings – Mulching or discharging your clippings is not a good idea if you are running your mower without a muffler, especially if it’s dry and windy. If clippings get inside the exhaust, it can lead to backfiring or worse still, your lawn mower on fire. Bagging your clippings reduces the chances of this happening significantly as the clippings aren’t left to blow around your lawn.

The Bottom Line

If your lawn mower’s muffler has broken off, and you absolutely need to mow the lawn before getting it fixed, it should generally be safe to do so. But mowing time should be kept to the absolute minimum and a replacement muffler should be sourced and installed as soon as possible.