The chain revolves around the chainsaw guide bar at incredibly high rates of speed, often in excess of 50 ft per second. With these speeds comes an enormous amount of friction. To prevent damage to the guide bar, chain and clutch, a continuous supply of bar oil is required for all chainsaws. Without this oil the bar and chain will heat up rapidly and damage the chainsaw.
Bar and Chain Oil
Modern chainsaws are designed to cut with a lubricating oil designed specifically for use in chainsaws. The bar and chain oil is designed to stick onto the chain long enough to keep it lubricated. This oil is also designed to withstand the higher temperatures from the friction, especially at the bar's tip. Most chainsaw manufacturers produce their own bar and chain oils, however, any high quality bar and chain oil will suffice. Still all modern chainsaws do not recommend using anything except bar and chain oil. While bar and chain oil doesn't come with a Society of Automotive Engineers viscosity rating, in an emergency situation, a high quality SAE 30 oil can be used.
Using Other Oil
From the 1950s to roughly the 1980s, chainsaws were designed without an automatic oil pump. Bar and chain lubrication was done manually, either through a manually controlled pump or put directly on the bar and chain. However, this process was tedious and time-consuming. These chainsaws, because of their lubrication style, used regular automotive engine oil. Generally they used a thicker weight oil, around 5 to 10 SAE. So if your chainsaw was manufactured during these periods, automotive engine oil and bar and chain oil will both work.
Modern chainsaws haven't been designed to use automotive engine oils. Automotive engine oils, even the thickest, can't compare with the design of bar and chain oils. Simply, the automotive oils will not stick long enough to the bar and chain to provide adequate lubrication; they will be thrown from the bar due to the higher chain speeds. Bar and chain oil will stick longer and prevent overheating. Without this lubrication, modern chainsaw chains will heat up quickly and blow out the drive sprocket and clutch.
Most chainsaw manufacturers recommend blending the bar and chain oil for winter use. In temperatures below 40 degrees Fahrenheit, the bar and chain oil will be too thick and won't adequately lubricate the bar and chain. Add a little kerosene or 10 SAE oil to the regular bar and chain oil. Mix in up to 10 percent of kerosene or 10 SAE oil and mix it thoroughly with the bar and chain oil before putting it into the oil tank. Continue monitoring performance while cutting and adjust the mixture as needed.