Even if you have a relatively new lawnmower, a problem with a hot engine can happen to anyone at any time.
Here you are trying to finish mowing your lawn, it’s hot outside and you’ve stopped to empty the grass cuttings from your mower bag. You’ve stopped and unfortunately, so has your lawnmower.
You may have run through your list of things to check on:
- Oil filter
- Air filter
- Sparkplug wire
and everything seems to be in order. In the meantime, your lawnmower engine is cooling down a bit. Perhaps you activate it once again after it has cooled, and surprise! It starts up.
So, why won’t my lawnmower start when it’s hot?
Good question! Let’s consider some of the reasons your mower may not start up if its engine is too hot. There are various other things that we can ask ourselves:
- Is the ignition coil working?
- Are the sparkplugs working?
- Are the sparkplug cables in good condition?
- Is your carburetor in good condition?
- Is the solenoid coil damp, or perhaps defective?
These are just a few of the many things that can influence if and how your mower engine functions.
The Do’s and Don’ts When The Lawn Mower Won’t Start When Hot
Dirt and Clogging
Is your mower engine overheating? Even though lawnmower engines can be relatively small, they do, nonetheless, produce quite a bit of heat when operating.
Your mower probably does have fins for heat dispersion and cooling, however, if bits of grass or soil clog the fins while mowing, they may not be operating to potential.
This will cause the engine to overheat because it has not cooled sufficiently. At this point, if your engine doesn’t cool down, it will not start.
A plastic lawn mower cover that houses the engine may also be collecting dirt, pieces of leaves, or twigs and this, too, could cause your engine to stop.
- Do wait until the Mower cools down completely. Do not work on it while it is still hot.
- Do remove the plastic housing cover and clean it thoroughly.
- Do clean the cooling and heat dispersion fins on the motor.
If debris is the cause, with a good cleaning, your mower should start up promptly.
The Correct Oil Level
Another reason your mower may not start might be attributed to the level of oil. Some mowers are sensitive to levels that are fill too high or on the contrary, too low. If the oil compartment has been overfilled it may block your engine.
Likewise, if you haven’t enough oil, the engine won’t work. Some manufacturers place a block feature on the lawnmower to protect it if the levels are wrong.
- Do check the oil level inside the motor.
- Do check how much fuel you have as well.
The Spark Plug
The first thing to check is the condition of the spark plug. Also, if you have recently changed the spark plug, make sure you have inserted the correct type of spark plug for your brand of lawnmower. You can experience a start failure if by chance you are using the wrong spark plug.
- Do check the spark plug model and code for your specific mower.
- Do check to see if the plug sparks before you proceed to replace it. Do not replace it if the spark plug is good.
- When buying spark plugs, do buy an extra one to keep on hand.
If the spark is poor, this can be indicative of several different problems:
- Your plug may be too worn
- Too large of a gap between the electrodes
- Something is wrong with the plug wire
As you probably know, the spark plug cable must make contact with the flywheel and the ignition coil. The flywheel, in turn, will make contact every time that it completes a turn to create the spark.
Perhaps the gap or spacing is too large here, just like in a plug. If you cannot make adjustments to the flywheel or coil, they may need to be replaced.
Keep in mind that often, the coil is enclosed in a unit that is sealed. In this case, no adjustment will be possible. Remember that the coil and the condenser will control electricity flow to the plug.
This is a common but easy problem to fix on the spot. If you haven’t ever tightened the lawnmower’s bolts, this could explain your problem. Engine parts are held together with bolts as the motor is fixed to the mower’s frame with bolts.
With use and vibrations, these bolts will loosen. Loosened bolts are a major cause of air leaks. These leaks will have your engine taking in too much air and this will upset the fuel-air ratio in the engine.
- Do tighten bolts holding engine components together and which fix the engine to the frame.
A Compression Problem
This problem can also be recognized relatively quickly. If the mower’s ignition cord moves too easily, you may have lost adequate compression. The clearances for the valves may be too large.
If this happens, we recommend an authorized repairman, as this is an internal problem within the engine.
The Choke Sticks!
A carburetor choke will feed the engine with fuel as soon as you start the ignition. Should your choke stick, the engine may be flooded with fuel and without sufficient air.
- Do remove your air filter and either clean it or replace it.
- Do check the linkages of the choke and once you have removed the air filter, clean the choke.
- Do check to see if your model of lawnmower has a solenoid coil. If this coil no longer works, your mower will not start if it becomes hot.
Other Potential Problems
A few less common problems include:
- The alcohol content in the motor oil has too low of a boiling level. Place a non-metal shim between the carburetor and the engine.
- Check the fuel mixture you are using. The engine may be lacking in fuel and receiving too much air. You can increase the fuel mixture a bit to adjust.
- Check the type of fuel. Are you using the fuel type that the manufacturer has indicated or suggested ? If you use the incorrect type of fuel, it may not only stop your lawnmower from running but also void your mower’s warranty.
- Have you by chance turned your mower on its side recently? People will do this when checking or cleaning blades. This position may let some fuel run into the mower’s engine, flooding a cylinder and creating a problem similar to a choke problem. If the engine has been flooded with fuel, it will not start. This may require repair assistance depending on the manufacturer and model.
In this case, try to close the fuel tap. This will prevent fuel from flowing beyond the valve for shutoff. Now return the mower to its correct position and allow any fuel to flow out. Once completed, your mower should start up again.