There are a number of factors that can prevent your lawn mower from starting, such as low fuel levels, incorrect start settings and a bad spark plug. One other factor that can be easily overlooked is oil, which serves as the engine's lifeblood. Depending on what type of lawnmower you have, it's possible that the oil levels are hindering a start.
Low Oil Level
For some models, it's possible that a low oil level will completely prevent your lawn mower from starting. This depends on your model's electrical system. If your mower has a low oil sensor that's integrated with the oil reservoir, that could signal the start system to prevent your engine from turning over. Otherwise, a low oil level may not prevent a full start but your engine may not run very long before seizing.
After examining oil's function in your mower, you can see how low oil levels can do serious damage. Oil is a lubricant for the engine's moving parts such as the pistons and piston rods. These metal parts, when active, are constantly touching each other and creating wear patterns. Oil keeps the parts from wearing directly on each other, which can cause them to break over time. Oil also can serve as a coolant since combustion generates heat inside the engine. Additionally, oil keeps the engines clean from any contaminants and debris.
Lawn mower manuals typically suggest checking your oil levels before every start and every eight to 10 operating hours. To do this, first make sure your mower has cooled down or hasn't started. This ensures that any oil spread throughout the engine has returned to the oil reservoir. Locate the oil fill port cap, which is usually on the top or the engine's side, depending on your mower type and model. Unscrew the cap and remove the dipstick, which has a level indicator at the end. Wipe the oil off of the dipstick and then put it back in the fill port without touching any of the port's sides. Slowly pull the dipstick back out and look at the indicator. There should be a "full" and "add" line, respectively. If there's no oil near the full line, you need to add oil.
Not all mower engines have the same oil capacity. Honda's push mowers can hold a little more than half a quart in oil, while riding mowers like the John Deere L2048 can hold 1.75 liters. It's best to add oil slowly when servicing or changing. A slow flow prevents oil from spilling into the combustion chamber. When combustion occurs, the oil can catch on fire and start to smoke. Oil can also spill into the exhaust system, where it will also burn and smoke.