Choosing the Right Oil for Your 4-Stroke Lawnmower Engine

When it comes to maintaining your 4-stroke lawnmower, one of the key components to ensure its longevity and performance is the choice of oil. Whether you have an owners manual or need to research your specific model, this guide will help you determine the best oil for your mower engine.

Using the Factory Recommended Oil

It is always best to follow the manufacturer's recommendations for oil in your 4-stroke lawnmower. If you have the owners manual, it will specify what type and grade of oil to use. If not, you can look up your mower by name and model number on the internet to find the appropriate manual and see the recommended oil.

Amsoil vs. Standard Oil

I have been using Amsoil Interceptor synthetic 2-stroke oil in the crankcase of a Kohler-powered mower for years. I mix it at a ratio of 40:1 for total loss burn-off, achieving great results. However, this oil is significantly overkill for a 4-stroke engine. The Amsoil oil is excellent for 2-stroke engines but may be more than necessary for a 4-stroke engine.

SAE 30 as the Standard for 4-Stroke Engines

SAE 30 is the standard weight of the oil used in 4-stroke engines for petrol lawnmowers. This oil type changes its viscosity based on the temperature, making it suitable for both cold and hot conditions. SAE stands for the Society of Automotive Engineers and is a standardized rating for oil used in 4-stroke engines for lubrication, cooling, and reducing friction.

SAE 10W-30 and 5W-30 Variants

If you are looking for slightly easier starting when the engine is cold, you can use SAE 10W-30 or SAE 5W-30. These are synthetic variants that provide better performance and protection, although they are more expensive. The 10W-30 has a lower viscosity when cold, making it easier to start, but it performs similarly to SAE 30 when the engine is hot.

Mixing with 2-Stroke Oil

While it is common to use SAE 30 or SAE 10W-30, I have rigged my free Kohler motor to work on Amsoil Interceptor 2T oil. I run a portion of this oil through the crankcase and mix it with gas at a ratio of 40:1, then top off with Amsoil 2T. This combination works great for me with no issues, and I mow around 2 acres each summer. The Amsoil synthetic interceptor 2T oil, while excellent for 2-stroke engines, is more than the motor requires.

To summarize, for a 4-stroke lawnmower, SAE 30 is the standard, while SAE 10W-30 or SAE 5W-30 are synthetic variants that can offer better cold-start performance. Always refer to the manufacturer's recommendations for the best compatibility with your specific mower model.

Remember, the choice of oil can significantly affect the performance and longevity of your lawnmower. By following the manufacturer's guidelines and understanding the differences between SAE 30 and synthetic variants, you can ensure your mower operates at its best.