Why is My Lawn Mower Leaking Oil?
Your lawn mower is likely leaking oil because of a worn-out gasket, loose seal, or overfilled oil reservoir, all of which can be easily checked and fixed. Other common culprits include faulty valve gaskets, damaged oil fill seals, or a misaligned lower or upper bearing ring seal. Identifying the specific issue will help you stop the leak before it leads to engine damage.
Fortunately, you don’t need to be a lawn mower mechanic to understand why your mower is leaking oil. The team at Mowrator has put together this guide to help you grasp the function of each component, so you can easily identify the problem and fix any oil leaks.
Other Signs a Lawn Mower is Leaking Oil
You may also be asking, “Why is my lawn mower smoking?” or, “Why is my lawn mower spitting oil?” These are further signs of loose components that are either damaged or not functioning due to improper fitting. A lawn mower that spits oil points to a more serious problem within the machine, while smoking from a lawn mower indicates that oil is dripping on a heated component.
Common Reasons for a Lawn Mower Leaking Oil
| Rank | Cause of Oil Leak | Description |
|---|---|---|
| 1️⃣ | Cracked or Worn Gasket | Gaskets (e.g., crankcase, valve cover gaskets) wear out over time (the most common cause of oil leaks) |
| 2️⃣ | Overfilled Oil | Too much oil can leak from seals, vents, or the muffler |
| 3️⃣ | Loose or Damaged Oil Drain Plug | A loose, stripped, or cracked drain plug or washer |
| 4️⃣ | Tipped Mower | Mower tilted incorrectly, especially with the air filter down |
| 5️⃣ | Leaky Oil Seal | Seals around the crankshaft or other engine parts can wear out |
| 6️⃣ | Cracked Oil Tube or Reservoir | A cracked oil fill tube or dipstick tube |
| 7️⃣ | Blown Head Gasket | A serious issue that can cause oil leaks, smoke, and loss of engine power |
| 8️⃣ | Worn Piston Rings or Cylinder | If piston rings or cylinders are worn, oil can enter the combustion chamber and burn off |
| 9️⃣ | Cracked Engine Block or Crankcase | A crack in the engine block can cause continuous oil leaks and require major repairs — a rare but serious issue |
Lower Bearing Ring Seal
Your mower has a crankshaft fitted through the bearing, and these two components are responsible for turning your mower blade. The bearing is also fitted with two seals, one on top and the other one on the bottom.
The lower bearing ring seal is usually responsible for an oil leak on your mower if it’s worn or loose. Replacing the lower bearing ring seal or fitting the existing one properly will often solve the leak.
Upper Bearing Ring Seal
The same can be said about the upper bearing ring seal. Check to see if yours is worn, damaged, or loose, and solve the problem by replacing it. Do not remove your bearing ring seals without the proper bearing seal removal tools, as this can damage them.
Valve Gasket
The valve gasket also serves as a seal between your gasket chamber and the valve cover. Look closely to see if there is some oil on the exterior of the chamber. If you do see a collection of oil and dust, this typically means your gasket is worn out.
However, to be sure it’s the valve gasket and not something else, clean the oil away, run your mower for 2 minutes, and check again. If the oil has reappeared, it’s most likely your valve gasket.
Oil Fill Seal
Your mower should have an oil fill tube where you can replace old oil with new oil. Check the seal of this fill tube to ensure it is fastened correctly and not worn. If it is, you’ll have to replace it.
Oil Fill Tube
The tube itself may also be damaged, although this is a less common reason for oil leaks in lawn mowers. The oil fill tube is located against (usually above) your crankcase. Wiping away the oil and turning on your mower for a couple of minutes before checking again, will give you an indication if the fill tube needs replacing.
Crankcase Gasket
Your lawn mower engine likely has a gasket that connects the two halves of the crankcase instead of just sealing a cover. This connecting seam is usually near the bottom or runs diagonally from back to front.
Once you see it, check for an oil buildup. Wipe it away, run your mower again, and switch it off before looking to see if the oil has re-emerged. If it has, this is likely the cause of your oil leak.
Why is My Lawn Mower Leaking Oil from the Exhaust?
Oil that leaks or spits out of your lawn mower’s exhaust may be a result of overfilling the oil fill tube, a blocked air filter, or worn-out parts. Exhaust oil leaks can also be caused by how you store your lawn mower when it’s not in use.
A clogged-up air filter causes pressure that forces oil from the engine to the exhaust. It’s a good idea to keep an eye on your air filters as well as any other replaceable mower parts, as replacing components usually solves the problem, but only if done correctly.
Remember to store your lawn mower flat on the ground, and don’t tip it to fit it into narrow spaces. Mower exhaust oil leaks are often caused by careless storage methods, so make sure yours is always stored safely.
Why is My Riding Lawn Mower Smoking?
Smoke from a riding lawn mower could be caused by a loose or damaged oil drain plug, damaged piston rings or cylinder, or oil leaking onto the muffler. Older mowers that have been serviced multiple times typically need the oil drain plug to be replaced every few years. Moreover, when piston rings or cylinders wear out, they overheat and cause smoking.
Sometimes smoke coming off a mower is nothing more than a short-term problem. For example, if oil happens to leak onto the muffler, it will smoke for a while but eventually burn off and stop.
How to Fix a Lawn Mower Leaking Oil
Step 1
Start by checking the oil level and make sure there isn’t too much in there. Excess oil will cause smoking, spitting, and leaking, so always use the indicated marker on the fill tube to put in the correct amount.
Step 2
Next, examine the air filter to see if it’s clogged. You can tell if it is by looking for a buildup of dirt and grime. You can also remove the air filter and blow through it to see if it allows air to flow through easily. If not, replace it with a new one.
Step 3
Now you can check the drain plug. If your mower is fairly new, this plug should be intact and functioning, but over time they do wear out. If the drain plug is worn out, replace it.
Step 4
Finally, check the gasket for oil buildup. Wipe away the oil and switch your mower back on. You will immediately notice if the oil has returned.
If your mower still leaks oil after checking all of these components, you should take it to a mechanic. They will be able to examine the engine itself for internal damage or wear and tear caused by age.
How Serious is an Oil Leak on a Lawn Mower?
If your mower is consistently leaking oil after multiple uses, it’s likely a serious problem that needs to be addressed. Leaving the leak as it is, may cause further damage to the engine, and will cost you unnecessary replacement oil.
Remember that your lawn mower has an engine, so a blown head gasket or cracked engine block is always a possibility. Also, be sure to replace your piston rings and cylinder based on how often you use your lawn mower. These components will wear out over time, depending on what you use your lawn mower for.
If you’re looking for an easy-to-maintain lawn mower, get in touch with our friendly team for lawn care and equipment advice. Shop Mowrator's collection of remote-controlled lawn mowers today.
FAQs on Why is My Lawn Mower Leaking Oil?
Does a lawn mower leaking oil mean the engine is faulty?
Not always. In rare cases, a lawn mower that leaks oil could mean that the engine is damaged or even cracked. However, in most cases, leaking oil simply means that the piston rings are worn, or that one or more of the seals or valves need replacing.
What is the most common reason for a lawn mower leaking oil?
A cracked gasket is usually the most common reason for a lawn mower leaking oil. Because cracked gaskets are made from rubber, they harden and crack. Fortunately, they aren’t expensive to replace.
How much oil should I put in my lawn mower?
It’s always best to check your owner’s manual to know how much oil to put in. You can also look at the oil fill tube to see if it has an indicator marking on how much you should put in when refilling it.
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