Gasoline to oil ratio in a chainsaw

Working principle of a two-stroke engine

Two-stroke engines work a little differently. These engines, like four-stroke engines, have a crankshaft, connecting rod, and a piston that runs inside the cylinder. Then the differences begin. Let’s look at them step by step.

Two-stroke engine principle

The first and most important difference. the gas distribution system. The usual camshafts, valves and cylinder head are missing here. This function is performed by the so-called windows (exhaust, intake and purge) and the chamber in the engine crankcase.

No oil in the crankcase. In general, there is no. The engine oil for two-stroke engines is in a separate tank or mixed with fuel. There is oil only in the gearbox, which is often combined with a two-stroke engine.

Instead, the crankcase has a sealed chamber. As the piston rises, it creates a vacuum in the combustion chamber. An air-fuel mixture is drawn in through the intake port from the supply system.

Two-stroke engine piston with long smooth skirt

Chainsaw Basics: Fuel and Oil

Exhaust and scavenging windows on the cylinder walls. They’re closed by the piston body. When the piston descends after the mixture has been burned and under pressure, it opens the exhaust port just before the bottom dead centre. The exhaust gases partly escape and the pressure in the combustion chamber returns to normal. There is a blowout port just below.

The piston, moving down through the cylinder, creates pressure in the crankcase where the fuel-air mixture that got sucked in earlier is already there. And when it reaches the blow-off window, the mixture under the action of pressure pushes the remaining exhaust gases out of the cylinder and fills the combustion chamber.

The piston goes up and closes both windows. spark plug ignites the air-fuel mixture at the top dead center. The cycle begins anew.

Another significant difference can be called the absence of oil rings (compression only) and needle bearings instead of shells in the connections of the connecting rod to the crankshaft and piston. Also often lack of liquid cooling system. Motor is cooled by passing airflow.

Another visual scheme of the two-stroke engine

The advantages of the two-stroke engines are as follows:

  • Good power density factor (relatively high power per unit mass).
  • Easy to build.
  • Requires little maintenance.

Significant disadvantages include:

  • Relatively short service life and low reliability.
  • Relatively low efficiency.
  • High probability of overheating (for air-cooled two-stroke engines).

Air-cooled two-stroke engine oil is added to the fuel. This peculiarity imposes some restrictions on its properties. But we’ll talk about it later.

Dilute gasoline with oil is necessary to avoid engine failure. The reason for that are peculiarities of the two-stroke engines’ lubrication system. These engines are designed without engine oil chambers, and if you pour in fuel without lubricant, the crankshaft, piston, bearings, and connecting rods will not be lubricated. This will significantly reduce the service life of all of these parts, so do not pour pure fuel.

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Gasoline and chain saw oil should be poured in appropriate proportions, which enables effective lubrication of friction parts. Lack or excess of lubricant will lead to negative consequences in the form of carbon deposits. To make your tool work properly you should not only fill it up with high-quality materials from the first day of its use, but also follow the correct proportions.

For the engine to work properly, the main thing is to fill it with clean fuel without any impurities.

Risks of using fuel and oil surrogates

In the technical documentation on chain saws of any manufacturer you can find a warning that it is forbidden to fill the engine with biofuel and gasoline surrogate. This is due to the unstable characteristics of such fuel, which can significantly damage the engine and reduce its life. If you pour such a mixture into your chainsaw, it will remove the manufacturer’s warranty.

There’s also the risk of buying low-quality engine oil which, according to some estimates, accounts for 10-12% of the market. In order not to buy low-quality oil, it is recommended to use only trusted stores, preferably approved by the manufacturer of the chainsaw.

What is the best gasoline and oil for your STIHL chain saw: Correlation table, dilution and proportion

The durability and uptime of a chainsaw is determined not only by its operating conditions, but also by the quality of the fuel used for refueling. In addition to special running conditions during the first few fill-ups, you also have to pay attention to the quality of the fuel mix.

STIHL professional chainsaws are fitted with two-stroke engines that require a high-quality fuel mixture of high-octane gasoline and oil, designed for high engine speeds. Choosing the right gasoline and oil for your STIHL chain saw is the key to a long and successful STIHL machine.

What kind of gasoline to put in your chainsaw??

When choosing a proper gasoline, every tool owner should take into account the brand and country of manufacture of the currently used model. Old domestic-made saws called Ural and Druzhba are best fueled with AI-80 gasoline. It contains exactly those additives that are necessary for stable performance of fastidious local engines. modern domestic models are designed to run on 92 gasoline.

The situation is a little different with imported chainsaws. Motors of all these models are designed for gentler fuel, so German, Swedish, American and Japanese chainsaws should be filled only with gasoline, AI-92 brand.

The condition of the gasoline plays an important role in the choice. Many novice gardeners are convinced that the fuel tank of the saw can be filled with fuel that has been in the canister for a long time. Some believe that the tool already works in conditions of constant dust, and it is because of this that the carburetor manufacturers have provided a special air compensator, which is triggered when the air filter is worn.

This is an opinion that is fundamentally mistaken. As a result of a long stay in the canister gasoline loses its main properties, and its composition, depending on the material of the container, is replenished by molecules of plastic or metal rust.

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To avoid this, you should regularly use only fresh fuel from proven refueling stations. It is best to buy 2-3 liters of gasoline every morning before starting work in your garden. Using fresh gasoline will make it easier to start the chainsaw, and will greatly extend its operating life.

Fuels and lubricants


Engine manufacturers recommend using high-octane gasoline AI-92, 95. Do not use fuel with various octane enhancers. During this time in it may undergo tarring and polymerization process that negatively affects the operation of the engine.

It is not recommended to use gasoline that has been stored for more than 60 days

Most chainsaw engines are equipped with leaded gasoline. If you bought a tool with a catalytic converter (the cap of the tank will be green) we recommend unleaded brands of gasoline.

Important: Do not skimp and use gasoline with a higher octane rating than 90. Also do not use gasoline with an octane rating higher than 95. This leads to premature wear of the engine piston group.


Air-cooled, two-stroke engines are not designed with a separate oiling system. Moving parts are lubricated by the oil in the fuel mixture. That’s why you should only use high-quality oils from trusted manufacturers.

Recommended oils for chain saw lubrication:

  • STIHL HP. developed especially for chainsaw engines. Proven excellent in all weather conditions, ensures perfect engine performance.
  • Husqvarna HP oil from a well-known gardening equipment manufacturer. Special additives reduce fouling on the engine crankcase, which can occur due to the use of low-quality fuel.
  • Oleo-Mac Prosint 2T. multifunctional oil with synthetic esters. Protects engine parts from corrosion, reduces wear of mechanisms and parts.
  • Champion JASO FD is a quality oil from a well-known company. Provides good protection for all moving engine parts;
  • Vitals Semisynthetic is an all-season oil for budget models of chain saws, designed for use at temperatures from.20 to 40C 0.

Important: Do not use mineral, semi-synthetic, or synthetic car oils. They are designed for a different engine type and do not have the necessary properties.

What happens if you put used oil in a chainsaw?

When the chainsaw owner has used it for some time, he may want to make some modifications to the tool. And it’s good if his desires are limited to the purchase of various accessories that expand the functionality of a chainsaw. But some go further. they start experimenting with the gasoline and oil that their saw runs on.

gasoline, ratio, chainsaw

If we’ve already talked about gasoline (most modern saws require it with a high octane number. at least 92-95), then it’s worth talking about oil especially. Many motorists accumulate a lot of used engine oil over the course of using their vehicle. And that’s why some people get the urge to use this stuff to fuel a chainsaw.

gasoline, ratio, chainsaw

If you do that, you are guaranteed engine failure. The reason is mainly the low lubricating power of the reused oil. It will burn with great emission of black smoke. Metal particles in the oil will first clog the fuel filter (those are the larger particles), and then the cylinder o-rings will fail. The metal particles in the oil will also damage the surface of the cylinders and bearings themselves.

Some “innovators” try to use waste oil for lubricating the chain itself and the chain block, on which it is located. This will also do no good. What exactly would happen. you can see on the attached video.

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Recommendations for ingredients

Even a chainsaw owner who observes the proportion to the gram can harm his tool if he uses low-quality or inappropriate components. The general recommendation is to use special fluids.

Two words about oil

Oil for two-stroke engines is mainly produced for gasoline-powered household tools. It is always colored in some bright color. blue, green, red, pink. The reason for this is that when you add them to the gasoline it is clear that they are a ready mix that you can already pour into the gas tank. Major manufacturers, like STIHL, have several kinds of oil that are differentiated by color.

If you have a chainsaw for which the recommended oil is from the same manufacturer, follow this recommendation if you are a beginner. Only by trial and error do the experienced “sawyers” find the oil that suits them best.

Don’t put car engine oil in a two-stroke engine! Although the Internet is full of reviews of those who say “Iu, and the flight is normal”, believe me: they have not yet showed the master of the piston of his tool. And the smoke from the muffler is unlikely to please you.

and about gasoline

To say that in the oil industry and refining in Russia gasoline is mostly of poor quality. is to repeat the obvious. You can “get” in a bad fuel not only at an anonymous gas stations, but also at big gas stations with a big name. High-quality gasoline is very important for modern high-tech chainsaws. it allows them to work with maximum efficiency and minimum wear. Today, the general requirement is to use gasoline with an octane number not lower than 92. It has optimum values for chain saws.

It was possible to fill old Soviet aggregates with 76th gasoline. Today you should not do this, even with cheap Chinese saws. you will only accelerate its “death”. It is also not recommended to go to the other extreme. to pour 95 or even 98 into an expensive tool, thinking that it will be better for it.

The buyers come and ask: the better the gasoline, the better the saw? Why don’t you use 95?? In fact more advanced cars require only it.

The answer is that most of the Russian gasoline 95 is the same as 92, but with detonation reducing additives. This parameter is not important for a chainsaw, it needs the purest possible gasoline because additives are absolutely unnecessary. That is why the logic is simple: better pure 92 than more expensive 95, but with unnecessary additives.

Fuel mix for a chainsaw: how much oil per liter of gasoline

Any petrol-powered machinery will only perform properly if the rules of operation and proper fuel mixture preparation are taken into account. This peculiarity also applies to chainsaws. Let’s see in detail how much oil to use per liter of fuel and how to prepare fuel correctly.