8 Reasons Why Lawn Mower Hard to Start When Cold

Lawnmowers, like any power tools, are complicated pieces of machinery – and the problem with complicated machinery is that there is plenty that can go wrong. If you have a gas-powered lawnmower, one of the most common problems you might face is that it is hard to start. This is especially the case when the weather is cold.

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If you are finding you Lawn mower hard to start when cold, here are the steps you should take to identify the problem and then hopefully resolve it.

Eliminate other possibilities

If you are finding your Lawn mower hard to start and you suspect it has something to do with the temperature, the first thing to do is eliminate any other possibilities.

Here’s a video about trying to start a mower that’s been sitting for a while.

Many people jump to the conclusion that cold temperatures are to blame when, in fact, the problem lies elsewhere.

Just because it’s cold, that doesn’t mean this is necessarily the problem. If you are starting your mower for the first time in early spring after it has been sitting all winter, there are plenty of other reasons why it won’t start.  Here are some things to check first.

1. Are you out of gas?

Extremely obvious, but worth mentioning all the same. The first thing to check if your mower won’t start is the fuel. If you are sure you have gas in the tank, you can move onto other things.

2. Are the gas lines clear?

Sometimes fuel can become contaminated with debris or anything else that falls into the tank. If you run out of gas, this may be sucked into the gas lines and prevent the engine from starting. Check the gas lines are clear of debris to eliminate this possibility.

3. Old fuel in the tank

Gas doesn’t age well, and if you have left fuel in the tank for a long period or over winter, you will probably have problems starting it again. If this is the case, empty the tank and refill it with fresh fuel to see if this solves the problem.

4. Check the spark plugs

Another reason why a mower won’t start is that the spark plug is not fitted correctly, is dirty or is just old. Check to see that it is correctly in place, and if it is dirty, give it a clean. Changing spark plugs every year is not expensive and can help avoid these kinds of problems.

Applying some starter fluid to the tip of the spark plug may also help with starting stubborn mowers. Also check the wires are all connected correctly.

5. Check the air filter

A clogged air filter may also prevent a mower from starting. Make sure it is clean and free of debris and try again. If it is very dirty, you may consider installing a replacement.

6. Check the ignition switch is in the “on” position

After leaving your mower in the shed all winter, you may have forgotten exactly how it works. Check the ignition switch is in the “on” position and also that any safety mechanisms are disengaged.

If it’s none of these, what to do next

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If you check these and other obvious reasons why your mower isn’t starting, your suspicion that it won’t start because it’s cold might well be correct. In this case, there are a couple of other things to look at

7. Is the oil you are using suitable for cold weather?

One possibility is that you might need to look at the type of oil you are using in your mower – and this is true of a riding Lawn mower as well as other types of gas-powered models.

Temperature affects the viscosity of oil – this means oils are thicker when cold and thinner when warm – and different oils are better suited to different temperatures.

For this reason, it may be the case that oil that works fine in the warmer summer months will not be able to do the same job in colder conditions.

Choosing the right oil also depends on your engine. For example, SAE30 is a single-grade oil that works well in older engines at temperatures of 40-100°F, while multi-grade oils work better in modern engines and have a wider temperature range.

If you are running an older engine type and are using a single-grade oil, you may have to consider changing the oil depending on the time of year – this is what car owners used to have to do before the development of multi-grade oils.

At the start of the year, when conditions are still cold, trying to use a single-grade oil that is more suitable for warmer temperatures could well be the reason you have trouble starting your lawnmower.

Try replacing it with an oil that works well in cold conditions to see if this solves the problem.

If you are trying to start an engine in more extreme conditions of cold, specialist oils exist that will allow you to do so, even in temperatures well below freezing.

Another thing to try is simply changing the oil. If you haven’t done this for a while, this may also resolve your problem.

8. Valve problems

If you have eliminated everything else, you may have a problem with your valve. Heat causes metals to change size and shape, and a valve that works well when heated may not work properly when cold, making the engine difficult to start.

This is a more difficult issue for a casual gardener who doesn’t know their way around engines to identify and fix. If you know what you’re doing, this is another thing to check out – but if you are unsure, it might be better to call in a professional.

Many reasons – check them off one by one

As always, when trying to establish what is wrong with an engine, you should start at the simplest, most obvious possibilities and systematically eliminate them one by one. This will allow you to locate the problem – and once you have found the problem, you can take steps to rectify it.

Many reasons why a mower won’t start when cold are easy to fix, but if you can’t find or solve the problem yourself, it might be time to call someone who is qualified to check it.

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