Riding Lawn Mower Won’t Start—What Could Be Wrong?

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You hop on your lawnmower, ready to spend your time mowing your lawn, only to realize it won’t start. What could be the issue? Well, fortunately for you, we’ve researched in-depth the reasons your lawn mower won’t start and have some possible answers for you.

Your riding lawn mower not starting could be because:

  • It’s out of gas.
  • The gas is stale.
  • It has a bad battery.
  • Bad alternator.
  • It has a bad starter motor.
  • The oil level is low.
  • There’s a problem with the ignition switch.
  • The engine has seized. 

We’ve given you several reasons that could be preventing your riding lawn mower from starting. However, you should keep reading as we elaborate on each one and give you ways to diagnose each issue. Additionally, we’ll go over some other questions you might have about your lawn mower starter or battery.

A happy young man riding a lawn mower at a sunny summer day, Riding Lawn Mower Won't Start—What Could Be Wrong?

Out of Gas

Just like cars, lawnmowers can run out of gas too. Fortunately, the easiest problem to diagnose is whether there is gas in your lawnmower. So, is it possible the tank is low on your mower? Some gas tanks have a dipstick that you can use to check the fuel level. If it’s low, try topping it up and then try to start your lawnmower again.

Gas is Stale

If the gas isn’t low but has been sitting in the tank a long time, this could also be an issue. Gas that has been in the tank a long time without being used can become stale.

One of the easiest ways to tell if your gas is stale is to open the gas tank and smell it. The gas will smell like varnish instead of gas, and its appearance will also be different. Stale gasoline will look muddy or darker than it originally did.

Bad Battery

A car terminal battery corrosion

If the gas isn’t to blame, the problem could be with the lawnmower’s battery. You can check whether a lawn mower’s battery is dead by using a multimeter. Multimeters are used to test electrical voltage, currents, and resistance.

The multimeter will let you know the voltage of the battery in your lawnmower. If it’s 12.7 volts or higher, the battery is fine, and the problem lies elsewhere. If it is below 11.5 volts, you will need to replace the battery with a new one. Sometimes the reading may be between 11.5 and 12.7. If this is the case, the battery may just need charging. 

Click here to see Multimeter on Amazon.

How long do riding lawn mower batteries last?

Riding lawn mower batteries typically last around 3 to 4 years. Once a battery passes this point, you’ll likely start to encounter issues with it. Your lawnmower might begin to lose power, and eventually, it won’t start at all. 

How much does a riding lawn mower battery cost?

over the top of a riding lawnmower into tall grass and weeds

Lawnmower batteries will typically cost between $50 and $75. However, there are more expensive and cheaper options available depending on the type your mower needs. 

Click here to see Lawn Mower Battery on Amazon.

Bad Alternator

There are several signs you can look for that might point to the alternator of your lawnmower being a problem. If your battery keeps dying, but the battery itself is fine, the alternator might be to blame. You can also test the alternator with the multimeter device we mentioned earlier. Your owner’s manual should tell you what reading you should achieve from the multimeter. 

You can also test the alternator by performing a test using the headlights. If you turn on the lights and then turn off the power to your lawnmower, the lights should dim. If they do not dim, there is a problem with the alternator. Alternators typically go bad due to overheating. Think back to whether you’ve been running your mower for long periods of time, as this could be to blame.

Bad Starter Motor

Once you’ve tested the alternator or battery and found they aren’t the problem, you should switch your diagnostics to check the starter motor. The starter motor is the connection between the battery and the lawn mower’s ignition system.  If you are having any electrical issues that can’t seem to be ruled out as issues with other parts, the starter motor may be to blame.

What are the Symptoms of a Bad Starter on a Riding Lawn Mower?

Symptoms of a bad starter on a riding lawn mower include the lawn mower not starting or clicking or cranking noises coming from the mower when you try to start it. The most obvious sign you have a problem with the starter motor will occur when you turn the key. If you turn the key and it makes a noise, but the engine doesn’t start, it’s likely the starter. 

How Do you Test a Lawn Mower Starter?

You can test a lawnmower starter using jumper cables. Before you attach the jumper cables, make sure to brush off any dirt or debris that might have accumulated. This will help promote the best possible electrical connection.

Once you have attached the jumper cables, the starter should turn over. If it doesn’t, you will need a new starter motor. If the starter does turn over, this likely isn’t the part of the mower that is preventing it from starting. 

Sometimes it’s easier to see the process done to understand what you have to do, so if you’d like to see a video on how to test a lawn mower starter, check out this handy YouTube tutorial:

How Do you Start a Riding Lawn Mower with a Bad Starter?

So what if your starter is bad, but you desperately need to mow your lawn? Well, unfortunately, if your starter is truly bad, you can’t. You will need to replace the starter before you try to mow your yard.

However, first, you should make sure that it is definitely the starter causing you problems and not the battery or alternator. You can also try cleaning any dirt and debris from the parts to see if that is causing interference. 

Low Oil Level

Engine oil reaches full level on car's dipstick against grass background

If the issue with your mower doesn’t seem to be electrical or gas related, it could be your oil level. Many ride-on mowers, especially newer models, will not start if the oil level is too low. This is in order to prevent damage to the engine of the mower.

Your lawnmower should come with a dipstick in the oil tank so you can check the level. Wipe the dipstick clean and reinsert it. Remove it again to see the current oil level.

If your oil is, in fact, low, check your owner’s manual to see which type of oil your mower needs, and follow the instructions for adding oil to your machine.

Click here to see Engine Oil on Amazon.

Problem with the Ignition Switch

If you’ve noticed your lawnmower stalling during previous uses, this could indicate you have a problem with the ignition switch. It can cause the engine to stall and then be the reason it won’t start later on.

Just like the battery and the alternator, the ignition switch can be tested using a multimeter to measure the ohms of the switch. To measure the ohms of the switch, the multimeter should be set to resistance mode. 

Here’s a YouTube video showing you a way to test your ignition switch:

Seized Engine

If your lawnmower has been sitting in storage for a long time, it might have a seized engine. A seized engine will prevent the mower from starting. Engines can seize due to low oil levels or from being exposed to the elements too long.

Fortunately, there are methods you can try to unseize an engine. Depending on how bad the engine is, it may require more complex methods to unseize it, and you may need a professional. However, if this doesn’t work, you will likely have to replace the mower entirely. 

The most simple method involves removing the engine’s spark plug and using an engine lubricant to help unseize the engine. After you have got the engine moving again, you should replace your engine’s oil to help prevent it from happening again. 

Click here to see Engine Treatment on Amazon.

If all of this seems a little overwhelming, don’t hesitate to call a professional to take a look before completely giving up.

Final Thoughts

A happy young man riding a lawn mower at a sunny summer day, Riding Lawn Mower Won't Start—What Could Be Wrong?

As you can see, there are a lot of issues that could be preventing your lawnmower from starting. Hopefully, with the help of our article, you are one step closer to figuring out the problem with yours. Fortunately, most of the issues are relatively easy to check for, so you should be on your way to a running mower again soon! Good luck!

For more reading on similar topics, check out some of our other blog posts:

Do Starters Go Bad From Sitting?

Ignition Key Hot When Removed – Should I Do Anything About It?

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