Riding Lawn Mower Won't Start? The Answer May Be In Your Oil

Despite not wanting to, you pick a sunny day to mow your lawn. But when you try starting it, your riding mower either doesn't comply or sputters out within a few minutes. Now, you might not worry much if your equipment was on its last legs anyway and you were planning on replacing it. However, if it was brand-new or you only bought it a couple of years ago, you may get concerned. Though there can be a myriad of things wrong to explain why your mower won't start, the answer might just be in your oil. To elaborate, if there's no or very little oil left in your machine, it will face issues.

If you're lucky, the problem will be limited to your riding lawn mower not starting. Keep in mind, however, that this will happen only if there's a built-in low-oil shutoff valve – a safety measure found in certain newer models. Other times, it'll start, with the internal components overheating within a few minutes (no longer than five). It happens because lack of oil will lead to increased friction between the moving parts. This, in turn, will cause the engine to seize (the parts inside – piston and cylinder – begin fusing together), cutting the life of your mower dramatically short.

Though this might not seem like a big deal, a damaged engine with welded parts is generally non-salvageable. So, to avoid damaging your precious (and expensive) riding lawn mower inadvertently, always check the oil level with a dipstick (note, a dipstick is sometimes attached to the oil fill cap) before you try starting it. Follow the manufacturer's instructions to get the right reading for your machine.

Though checking the oil level before you start your riding lawn mower is a great way to ensure you don't damage it, you might not always be willing to spend those few extra minutes doing this. In such scenarios, take cues from your mower. One of the first things to keep an eye (read: ear) out for is any irregular loud banging noise. Caused by the internal components rubbing against each other, it's akin to a warning bell. You might also hear some knocking sounds coming from the engine as it keeps running.

You can still salvage your equipment at this stage if you turn it off as soon as possible (preferably within 30 seconds of starting it). Yet, there's still a slim chance that it'll seize once it cools down. So, you're not completely off the hook even if you take immediate action. However, if you're beyond the 30-second mark, your riding lawn mower will let out a loud screeching noise, as it continues overheating and the parts weld together inside. This may be accompanied also by a burnt smell, like that of oil or metal being ignited. By this stage, it will be incredibly difficult to reverse the damage, and there's a non-zero chance your lawn mower engine will last long after this.

Before you decide to replace the engine, or spring for a new riding lawn mower altogether, it's good to be certain whether your mower's engine has seized or not. For a riding lawn mower today, there's really only one way: to test the blade, as starter cords were phased out decades ago. (That said, if your machine has a starter cord/rope, with a seized engine, you simply wouldn't be able to pull it.)

To test the blade, wait for your machine to cool down, then take the ignition key and spark plug wire (the L-shaped rubber piece to the side or front of the engine block under the hood) out. Now, elevate your mower using a ramp or a lift jack – a riding lawn mower weighs anywhere from 300 pounds to 800 pounds, depending on the size. After you lift the machine, remove the deck, and try rotating the blade by hand. In case it moves freely, you're in the clear. If not, the engine is probably seized and will need attention. 

At this point, you can either fork out anywhere between $500 and $1,800 on a new engine (though you stand to save a little on labor costs if you undertake the project yourself). Or, you could buy a new mower for your yard.