Why is My Lawn Mower Leaking Oil onto Deck? Causes & Repair

Hello, as a landscaper, I’m here to explain the reasons behind the oil leak from yours. Let’s start by outlining the key components in the lawn mower that could be causing the lawn mower to leak oil onto the deck, and then consider common issues specific to your lawn mower model that might contribute to the problem.

Finally, I’ll recommend repairing the leak, including any necessary parts replacement, troubleshooting steps, or possible repair costs associated with the issue.

Essential Components that Could Cause an Oil Leak

  1. Engine: The engine is the primary source of oil in your lawn mower. The oil circulates to keep the engine running smoothly and prevent overheating. If there is a problem with the engine or its oil circulation system, you might experience a leak.
  2. Oil Filter: The oil filter assists in removing contaminants from the oil, keeping it clean, and maintaining engine performance. A damaged or obstructed filter may cause oil leakage.
  3. Gaskets: Gaskets are essential for sealing several components of your lawn mower’s engine, preventing oil from leaking. Worn or damaged gaskets are among the most general causes of oil leaks.
  4. Oil Seal: The oil seal is a crucial component in preventing leaks. It separates the oil-filled areas from other lawn mower parts, like the air and fuel intake systems. If the oil seal has been compromised due to wear and tear, the oil may leak from your lawn mower.

Common Issues: Contribute to an Oil Leak on the Lawn Mower

  1. Improper Use: Oil leaks can be caused by lawnmowers operating on uneven terrain or at extremely high or low temperatures. This stress can compromise the oil seals and gaskets, leading to leakage.
  2. Wear and Tear: Regular lawn mower use will inevitably lead to wear and tear on its components. With time, seals and gaskets may become brittle and lose their sealing capabilities, resulting in oil leaks.
  3. Poor Maintenance: Neglecting regular maintenance, such as oil changes, filter replacements, and thorough inspections, can cause various components to become worn or damaged, increasing the chances of oil leakage.

Recommendations for Repairing the lawn mower leaking oil

  1. Inspect the Key Components: Inspect the engine, oil filter, gaskets, and oil seal for signs of damage or wear. This might involve disassembling some parts of your lawn mower, so consult your owner’s manual or a professional mechanic if you’re unsure about the process.
  2. Replace Damaged or Worn Components: If you find any damaged or worn components, be sure to replace them as soon as possible. This might include new gaskets, an oil seal, or an oil filter, depending on the source of the leak.
  3. Perform Regular Maintenance: To prevent future oil leaks, perform regular maintenance on your lawn mower. This includes changing the oil according to the manufacturer’s recommendation, checking and replacing the air filter and spark plug, and lubricating necessary components.

How to Fix a Lawn Mower Leaking Oil From Bottom? (Step-By-Step Method)

If your lawn mower leaks oil from the bottom, don’t worry – it’s a common problem many people face. This section will provide you with a comprehensive and detailed step-by-step method to fix this issue. Remember that you should always follow safety precautions when working with machinery. Let’s get started!

Tools and Materials Needed

  • Socket wrench and sockets
  • Screwdrivers (flat-head and Phillips-head)
  • Adjustable wrench
  • Needle-nose pliers
  • Drain pan
  • Funnel
  • Shop rags
  • Gloves
  • Goggles
  • Replacement oil seal (if applicable)
  • Lawnmower engine oil
  • Teflon tape (optional)

Step 1: Disconnect the spark plug

Remove the spark plug wire to ensure that the engine cannot accidentally start while you’re working on it. This is a critical safety step.

Step 2: Check for the source of the leak

Clean any oil residue from the bottom of the engine with a shop rag. Start the mower and visually inspect where the oil leak is coming from. Common sources of oil leaks include the oil drain plug, oil fill tube, and oil seal.

Step 3: Fix a leaking oil drain plug

  1. Place a drain pan under the oil drain plug.
  2. Loosen the oil drain plug with a socket wrench.
  3. If the plug is damaged or the threads are stripped, replace the plug. If not, wrap a few layers of Teflon tape around the lines to help create a better seal.
  4. Tighten the plug back with the socket wrench, careful not to overtighten it and strip the threads.

Step 4: Fix a leaking oil-fill tube

  1. Locate the oil fill tube and check for any cracks or damage.
  2. If the tube is damaged, replace it. Refer to your lawn mower’s owner’s manual for the correct replacement part.
  3. If the O-ring is damaged or missing, replace it and ensure a secure fit to prevent oil leaks.

Step 5: Fix a leaking oil seal

  1. Check the oil seal around the crankshaft near the bottom of the engine.
  2. If the seal is damaged or worn, it must be replaced.
  3. Remove the crankshaft pulley from the engine by loosening the retaining bolts with a socket wrench.
  4. Use needle-nose pliers to remove the old oil seal carefully.
  5. Clean the seal area and apply a thin coat of oil to the new seal.
  6. Install the new oil seal, ensuring it’s flush with the engine’s surface.
  7. Reinstall the crankshaft pulley and tighten the retaining bolts.

Step 6: Test your lawn mower for leaks

Reconnect the spark plug wire, add oil if necessary, and start the mower. Check for any oil leaks and address them accordingly.

Cautions and Potential Hazards

  • Always wear quality gloves and goggles while working with machinery.
  • Ensure the lawn mower is on a level surface and secured adequately before working on it.
  • Disconnect the spark plug wire to avoid the accidental starting of the engine.
  • Avoid overfilling the machine with oil, which could cause leaks and damage.
  • Do not overtighten bolts, as this could cause the threads to strip.

Following the steps outlined in this article, you can identify and fix any oil leaks in your lawn mower, helping it run smoothly for years.

Safety is paramount when dealing with machinery, so always exercise caution while attempting repairs. If you need help or have questions about your lawn mower model, please refer to your owner’s manual or contact an authorized service center.


Oil leak lawn mower issues are common, but with some handy DIY repair work, you can fix them yourself. To do this safely, always disconnect the spark plug wire before working on the lawn mower and proceed cautiously. Inspect all critical components for signs of wear or damage and replace any damaged parts as needed.

Regular maintenance will also help prevent future oil leaks by ensuring that components are properly lubricated and functioning correctly. With a little care and attention, your lawn mower should quickly be free of oil leaks.

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