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The lawn mower is one of the best-known and most popular machines in the home garden. As soon as a combustion engine is used, you cannot avoid using engine oil for operation. But which one is the right one?

In a nutshell

  • Lawn mowers can have different lubrication systems with 2-stroke engines or 4-stroke engines
  • Which engine oil a 4-stroke engine needs can be found on the engine and in the operating instructions
  • Biological oils tend to "grow" when left unused for a longer period of time and are therefore only suitable for lawn mowers to a limited extent

Mixture or separate motor oil?

With regard to the right oil, there is an elementary difference, depending on which type of engine was installed. There are two different systems that use completely different functions for lubrication and thus also for engine oil:

  • 2-stroke engines: Lubrication by the fuel used via a fuel-oil mixture
  • 4-stroke engines: separate lubrication by engine oil separated from the fuel

Either a special 2-stroke oil or a conventional lubricating oil suitable for the type of engine in question is used.

2-stroke oil

If a special 2-stroke oil is required, it will be marked as suitable for mixing with the fuel and can be used for all 2-stroke engines. The only thing that matters is the correct mixing ratio for the lawn mower in question. Typical mixtures are:

  • 1 part 2-stroke oil to 25 parts petrol
  • 1 part 2-stroke oil to 40 parts petrol
  • 1 part 2-stroke oil to 50 parts petrol

The ratio to be mixed is normally specified on the type plate and in the manual.

Notice: Again and again one reads that other oils can also be mixed with the fuel. For the sake of your engine, however, refrain from doing so in order not to provoke damage due to a lack of lubrication.

The marking of motor oil

On the other hand, it gets a bit more difficult with the 4-stroke engine. Similar to the car and other combustion engines, the manufacturer clearly specifies which type of oil or which group of engine oils may be used. Typical designations are SAE 5W40 or SAE 10W40 or comparable. The individual digits stand for the following properties of the oil:

  • SAE = "Society of Automotive Engineers", name of the classification system for the oil
  • Number before the W: refers to the flow properties when cold, the lower the number, the "thinner" the product and the better the cold start ability of the engine
  • Number after the W: designates the flow properties in a warm (W) state, the higher the number, the "thicker" and thus more resilient the product

Attention: Some manufacturers specify a range of possible oils for the lawnmower. If you deviate from the range, the lubricating effect may be lacking or the engine may have starting problems.

Mineral oil or bio oil?

In terms of resource and environmental protection, the market also offers organic products based on rapeseed or other plants in addition to classic mineral oils. The big problem with biological oils is their tendency to harden when left unused for long periods of time. In the worst case, the oil can harden and the engine can become unusable.

frequently asked Questions

What can I do if bio-oil has solidified in my 4-stroke lawnmower?

In the early stages it can help to warm up the engine, e.g. with a heat gun. In most cases, however, this case is an issue for the specialist workshop.

Why does my lawn mower smoke despite the correct 2-stroke mixed oil?

Smoke indicates burning oils. Every 2-stroke smokes to a small extent. However, if the smoke is heavy, there is in all probability too much oil in the fuel.

What should I do if I don't know the oil/petrol mixing ratio?

If in doubt, use the usual mixture with the highest oil content, i.e. 1:25. If in doubt, you will have to accept a little more smoke and, in the long run, an oily carburetor. Therefore, be sure to ask your dealer or the manufacturer directly for the right fuel.

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