Oil leaks on any engine can be a major problem. Like your car's engine, your lawnmower's engine needs a sufficient oil supply for lubrication and cooling. Running a small engine with too little oil will rapidly produce internal damage that will likely be far more challenging and expensive to repair than a simple oil leak.
Fortunately, it's usually relatively easy to spot oil leaks on a lawnmower. It's a good idea to give your mower a good cleaning several times per season, during which time you should check for signs of oil leakage above and below the deck. If you notice any oil spots, these three steps will help you understand the problem and decide on the best course of action.
1. Check the Oil Level
Anytime you spot oil leakage on your mower, stop the engine immediately and check the oil level. If the oil level is too low, it's probably a good idea to stop using the mower until you can resolve the issue to avoid causing engine damage. However, it's still important to address minor oil leaks. A small loss of oil can potentially damage your engine, in addition to posing an environmental hazard.
Of course, you'll also want to check if the engine oil level is too high. Too much oil can overpressurize the engine (a situation known as "back pressure"), potentially forcing oil through the exhaust or air filter. If you've overfilled your engine, drain it back to a normal level, run it again, and check for leaks.
2. Identify the Leak Location
If possible, attempt to identify the rough location of the oil leak. Leaks on the underside of the deck typically indicate a problem with the sump gasket, while leaks on the top can have numerous culprits. Check for signs of leakage around the oil filler cap, drain plug, dipstick, and filter. These are common failure locations and are usually fairly easy to repair with a new gasket.
On the other hand, extensive leaks or leaks that seem to originate from the engine itself will likely require a more substantial diagnosis process. While diagnosing leaks on push mowers is usually relatively straightforward, it may be more challenging to determine the location of a leak on a more complex self-propelled mower.
3. Decide on a Course of Action
While small lawn mower engines aren't as complex as those in modern vehicles, they can still be fairly challenging to diagnose and repair. If you can easily spot the leak's location and are relatively handy, attempting a do-it-yourself repair may not be a bad idea. However, blindly replacing gaskets and seals can worsen the problem or even introduce new leaks.
If you aren't entirely comfortable with your diagnosis or mechanical skills, leave any small engine repairs to a professional. Lawnmowers can be relatively large investments, and a mistake when dealing with an oil leak can potentially cause real damage to your lawnmower's engine.