Why is My Lawn Mower Spark Plug Covered in Oil?

Approx Reading Time: 7 minutes

Spark plugs in lawn mowers can occasionally get wet with oil or other fluids, and if you have never dealt with this before, it can be unnerving. This article will outline potential underlying causes of this to help you get your mower up and running again.

There are a few potential reasons for a wet spark plug in your lawn mower, but it’s most likely because the plug has overheated due to ethanol in the gas, and the combustion chamber is flooding with oil, or there is water flooding the engine or the fuel and oil tanks.

There are a few other potential reasons for spark plug flooding, and it may require servicing to thoroughly clean it. There are a few remedies that you can do yourself, as well as important precautions to take to prevent this from happening again in the future.

What Causes a Spark Plug To Get Wet With Oil in the First Place?

You may be wondering what happened to cause the wet spark plug in the first place. As I said above, the plug has overheated, and the chamber is flooded with oil, so your mower probably won’t start. You may not see it initially, but continuing to try and fire up your mower could cause long term damage to the engine.  

There are various reasons for spark plug flooding:

  • It may be due for a change. Spark plugs should be changed at least every two years, but sometimes sooner.
  • You may have used the choke too much and introduced too much fuel into the system. Beware of “priming” the mower too much.
  • The float may be stuck in the down position and not controlling the amount of fuel leaking into the engine.

Regardless of the chain of events that led to your mower not igniting, be sure to take note of these reasons for future reference. Always try to be up to date with servicing your mower and changing out old parts, and be sure to not flood the engine by priming it too many times when trying to start the mower.

Should I Fix it Myself, or Take it to a Technician?

You can certainly try to fix your mower by yourself if you feel comfortable with a repair. There are several steps to determine the specific problem with your mower, as well as ways to fix it.

You may have to make a few extra trips to your local lawn and garden store in the process, but the result will mean saving a considerable amount of money.

This being said, taking your mower to a technician is always a good step as they have the parts and fluids on hand. It will also mean just one trip to the specialist and it usually doesn’t take long.

You won’t have to deal with the potential cleanup of draining oil and gasoline from your mower or bother with tools required to disassemble your mower.

As with all appliances and machines, if you have something that costs more money, it is worth investing the capital to have a technician fix it such that you don’t create a more serious problem. 

But if you feel comfortable taking a few things apart and trying some of these quick fixes, you can save a lot of money in the long run.

How Do I Fix it?

There are multiple steps you can take to fix your mower. You’ll need to purchase starter fluid at your local home and garden store and possibly a new spark plug as well as fresh gasoline and oil.

Here are four steps you can take to fix the problem yourself that will save you money at a technician:

Starter Fluid

Take out the air filter and spray starter fluid down the carburetor. Be sure to turn off the choke before you do this. 

Start the mower if you can. If it does start, turn it off again and clean out the air filter before putting it back together. If it doesn’t start, move on to the next step.

Replace the Oil and Gas

Drain the gas and oil. As always, be careful about open flame near the mower or your person when doing this!

The easiest was to do this is by disconnecting the fuel/oil line and draining it into a bucket. If you don’t know where these are, or just aren’t comfortable doing this, you can also use a fuel transfer pump such as the Koehler Enterprises RA990 (buy on Amazon).

It’s also a good idea to remove the spark plug to prevent accidental ignition. Replace the oil and gasoline with fresh fluids and try starting it again.

If it doesn’t start, you may want to try replacing the spark plug.

Replace the Spark Plug

You may have to go back to the store for this since you likely wouldn’t have purchased one on your first trip, but you’re still saving a good deal of money. If the mower doesn’t start, move on to the next step.

Clean the Coil and Magnets

Turn the fuel valve to the “off” position and check the coil for rust. If it’s dirty, use sandpaper or a rough brush to clean it, and clean the magnets on the flywheel.

Replace the coil and make sure to tighten it to its original position.

How Much Does a Repair Cost?

Starter fluid is about $10 and usually the first item you will buy when first addressing the problem. A new air filter ranges from $10-$15 in case you decide to replace that as well, but usually starter fluid or draining the gas and oil will fix your problem.

If you have to replace a spark plug, they are not expensive, ranging from $5-$10 and sold in various lawn and garden stores.

Make sure that you bring the old spark plug with you to the store to talk to an associate to determine the exact right one for your mower.

If you take your mower to someone to do the repairs for you, the cost will be much more expensive than doing it yourself, but possibly a worthwhile price if you’re nervous about doing something like this at home.  The parts will usually range from $20-$25, and the labor will range from $60-$80, depending on where you live.

How Can I Stop This From Reoccurring?

A first and important step is to never leave your mower out in the rain. Rain can get into compartments and even the fuel or oil and cause the mower not to start.

Mowing wet grass after rain or early in the morning with dew can also lead to flooding the engine and should be avoided. Try to avoid over-priming the mower when starting it.

If you flood the engine with oil, then the spark may not reach the ignition, and you will not be able to start the engine. If you do this repeatedly, it will damage the engine or spark plug over time.

Be sure to replace your oil annually. If you consistently change the oil every 50 hours that you use it, you will keep it running smoothly and avoid fluid build-up that causes malfunction. 

As with all expensive pieces of machinery, keep track of how often you use it each year and be sure to follow best practice guidelines for replacing parts and fluids. 

Peter Toth

Hi! I'm Peter, the owner of BackyardGadget. Working around the house has always been a big part of my life. I've created this site to share my experience, and to help people choose the right tools for the job. Thank you for stopping by!