What Oil Should I Put in My Lawn Mower? Engine Oil for Lawnmowers Guide

Lawn mowers, much like any other combustion engine, require proper lubrication for their internal mechanical components to function efficiently and effectively. Engine oil serves as the sole lubricant necessary for your lawn mower's engine, playing a pivotal role in maintaining the health and performance of the machine. This essential fluid not only helps to cool the internal moving parts, but also provides vital anti-friction and anti-corrosion benefits that are crucial for prolonging the life of the engine. Without adequate lubrication, the friction generated by the moving parts can lead to overheating, excessive wear, and ultimately, engine failure.

It is crucial to develop the habit of regularly checking your lawn mower's oil level by reading the dipstick, before each use. This simple yet effective practice allows you to assess the oil level accurately and helps you notice any sudden drops in the oil level or changes in the oil's appearance that could indicate potential problems. By checking the oil level, you can prevent running the mower for an extended period in a low oil state, which can cause significant damage. A clean paper towel can be a useful tool in this process, as it allows you to observe any obvious changes in your oil's color and consistency, providing a quick visual reference to determine the oil's condition.

Typically, clean engine oil appears in shades of bronze or tan, indicating that it is in good condition and ready for use. In contrast, used or dirty oil will take on a black and sludgy appearance, suggesting that it has accumulated suspended contaminants in the oil, and should be changed. If you notice that the engine oil appears grey, this could be a troubling sign that indicates worn internal engine parts, which may require further investigation.

Additionally, it's important to keep the area around the oil fill hole clean and free from debris to prevent dirt or other contaminants from entering the oil sump, which contains the clean oil necessary for optimal engine performance.

Maintaining your lawn mower's cleanliness is a beneficial practice that goes beyond just aesthetics. As detailed in this post: They Say Cleanliness is Next to Godliness: and its No Different in Keeping Your Lawn Mower Clean!, a clean mower allows you to easily identify potential leak locations, whether they are related to oil or gas. If you check the dipstick and observe a significant drop in oil level compared to your last check, taking a quick look at a clean mower deck will enable you to locate the leak effectively. This proactive approach not only helps you determine if the leak is oil or gas, but also simplifies the troubleshooting process, making it easier to address any issues before they escalate.

If you observe a significant drop in the oil level compared to the last time you checked and notice a pool of oil that has collected on the deck, it is likely that there is an oil leakage problem that needs immediate attention. Pro Tip: If you cannot detect any signs of an oil leak on or beneath your mower's deck, be vigilant for white smoke while operating the mower. This might indicate an internal engine issue where oil is being consumed, leading to potential engine damage that could be more costly to repair than a simple oil leak. If however you have tilted your mower incorrectly, oil may be where it shouldn't and this too can cause a white smoke condition. If this is the cause, the smoke should eventually clear itself away.

Never operate your lawn mower without adequate oil in the safe range, as indicated on your dipstick, as failure to do so can lead to severe engine damage and costly repairs. Regular maintenance and vigilance in checking oil levels can save you from significant headaches down the road.

If you're uncertain about which oil grade to use for your specific lawn mower, it is essential to note that this post is not a substitute for your machine's operator's manual. Always refer to the manual for details specific to the make and model of the engine you're using, as different engines may have unique requirements that need to be met for optimal performance.

SAE-30 oil is typically recommended for small engines during summer use, as it provides adequate lubrication under warmer operating conditions. However, multi-grade oils like 10w-30 and 5w-30 are also appropriate choices for various temperatures. Notice the '30' in all these grades? It signifies that the oils have similar viscosity in summer, with slight differences in winter, as indicated by the '10w' and '5w' designations. A higher number means the oil is more viscous or flows more slowly. For example, using SAE-30 oil in a snow thrower is not advisable because it isn't suitable for cold starting and colder operating conditions. The oil would be too thick to flow properly in colder temperatures, potentially leading to rapid engine wear and premature failure.

It’s important to recognize that small engines are air-cooled and typically operate at higher temperatures than water-cooled automotive engines. SAE-30 weight oil is thicker compared to most automotive oils like 5w-20 or 0w-20, which means it is more resistant to breaking down under high heat conditions. This resistance is partly due to the fact that the heat generated by small engines, such as those found in lawn mowers, is generally greater than that produced by car engines, making the correct choice of oil even more critical.

Some contemporary OHV (Overhead Valve Engine) manufacturers even advise that full-synthetic multi-grade oils, which are commonly used in automotive applications, are suitable for their engines. Certain lawn mowers may have a decal located near the oil dipstick indicating which oils should be used, making it easier for operators to select the right lubricant for their machine.

Some lawn mower operators have noticed that using full synthetic oil makes it easier to pull start the mower due to reduced resistance or drag compared to SAE-30. Additionally, some users report that multi-grade oils tend to burn off more quickly than SAE-30 oil in higher temperatures, which can cause levels to drop faster.

Another important aspect to consider is the design and operational needs of two-stroke engines. These mowers require special two-stroke oils that must be mixed with gasoline in a specific ratio to ensure proper combustion and lubrication. Pro Tip: To determine if your machine is a two-stroke, look for an engine fill reservoir or dipstick. If neither is present, it is likely a two-stroke engine. All four-stroke engines have a separate oil reservoir and dipstick, which is a key feature that helps you maintain your mower correctly and efficiently.

This is an engine oil dipstick found on four-stroke engines

To check your oil, make sure the machine is on a relatively level surface, allow the machine to sit idle without running for a short while (if recently running), wipe clean the dipstick with a lint free cloth or rag, insert dipstick and take out to get an accurate reading; you want to be within the hash-marked section, preferably the higher end

It is important to point out that just because your engine oil dipstick is threaded, this doesn't mean that it must be threaded back into the engine cover, in order to get an accurate reading. You must consult your machine's operator's manual to determine in fact you must thread in the engine dipstick or simply press it into the engine fill tube hole. Sometimes the dipsticks themselves will be labeled with information about this. Failure to determine this can lead to inaccurate readings!

Hopefully after reading this post you have become familiarized with the basics of engine oil for lawnmowers, and are more confident in checking your own oil. This is an important skill in maintaining the service life of your equipment.

Never the Norm!