Why The Lawn Mower Won’t Start When Hot & How To Fix It?

We have all faced this trouble. Mowing for a while pretty great; then you stop it to empty the bag or refuel it – it won’t restart.

Until it cooled off, it won’t start no matter what you do. Lots of reasons may have contributed to this problem but the main culprit is most likely the failing coil.

It’s so frustrating when you checked the oil level, air filter, and so on but the lawn mower won’t start when hot. If you have a Briggs engine, you will face it a lot of times.

In this article, I will talk about the possible reasons and how to resolve the issue.

Why The Lawn Mower Won’t Start When Hot?

Apart from the failing coil, there are a lot of issues you need to check. From an overheating engine to the faulty carburetor, the mower may have a faulty plug and plug wire as well.

Even the vapor lock or the magneto winding may be going bad.

So, you need to check and recheck a lot of things some of which may sound childish but I strongly recommend doing so anyhow. Check the below-mentioned issues first:

  1. Overheated Engine

This is true for all kinds of motor engines. The lawnmower engine may look small but it generates a tremendous amount of heat when in operation.

To dissipate such extreme heat, it has cooling fins. But the problem is when you mow the lawn the grass clippings and other debris may clog the fins.

Since the clogged fins can’t dissipate enough heat, the engine gets overheated and stop. The engine won’t restart until the engine cools. The plastic housing can also collect dirt that will eventually lead to the engine shut off.

So, solve the problem you have to clean the fins and plastic covers once it is cool.

Lawn Mower Won't Start When Hot

  1. Low/High Oil Level

Some mower engines simply won’t start if the oil level is either low or high. The critically low or overfull oil tank won’t let the engine start. It may sound weird, but maybe your mower has run out of gasoline? Have a closer look!

To protect the engine, it is designed that way. So, every time you fill the gas, check the oil level regularly.

  1. Air Leaks

If you have never tightened the bolts that hold the engine components together and keep the motor to the frame, these bolts are probably loose now. This will make the engine of your mower shut off as well.

Let me explain how.

Loose bolts cause air leaks which in turn make the engine pull in excess air from the outside. That way the tiny parts of the engine expand as the engine heats up gradually.

Ultimately, you got a poorly running engine that will ultimately shut off.

So, periodically tighten all those bolts to avoid this problem.

  1. Problematic Spark Plug

Spark plugs come in a lot of variety. They have multiple heat ranges and lengths. There will be issues like hot start failures if you plug the wrong one into your mower. So, double-check the correct plug code that is suitable for your mower.

If I were you, I would keep a spare plug to deal with such cases.

  1. Problematic Compression

There is an easy way to figure out whether your mower is suffering from poor compression or not. If the mower’s starter rope seems to move easier than it used to be, it indicates the compression is poor along with too large valve clearance.

The compression issue is very common for mowers from Briggs and Stratton. If you are not a ‘techie’ person, call a professional small engine repair person.

  1. Malfunctioning Sticky Choke

The sticky chock located inside the carburetor should open up when the engine starts. But it won’t if it is malfunctioning and it will remain close to the engine.

Because of the lack of ample air, the engine gets flooded. Remove the air filter and clean the choke.

  1. Other Reasons Why Mower Won’t Start

Apart from the above reasons, there could several other reasons that may have led to this bad situation of yours. Sometimes it is the alcohol in the oil that is responsible because of the low boiling point.

You can solve the problem simply by placing a riser or non-metallic shim between the engine and the carb.

There could be some other reasons like the ignition coil may have gone bad though it is rare. But if the mower is 10+ years old, the chance is really high.

Now, watch the video tutorial on how to fix it when it won’t restart.


Next time you face the same problem like the lawn mower won’t start when hot, sit tight and have hot smoking coffee. Let the mower some time to cool down.

Being impatient won’t help at all. Then systematically approach to solve the problem checking every possibility I mentioned above.

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4 thoughts on “Why The Lawn Mower Won’t Start When Hot & How To Fix It?”

  1. Great insight regarding this issue…which unfortunately I am repeatedly experiencing. I replaced the thermostatic choke, cleaned carb, replaced the coil, tightened bolts, and replaced the keyway shim. I am about to replace the carburetor with a new one in hopes that will solve the issue. When the motor is running its like a swiss watch; runs great. Wish me luck!

  2. got Ariens 19.5 hp lawn tractor, after 10 or 15 minutes of mowing stops working, when cool down work again, changed ignition coil, spark plug, air filter, fuel filter, shut off solenoid, fan blade. Nothing. Funny story when I removed hood, no problems. Any ideas?

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