Engine Lubrication

• The two tanks on a chainsaw provide fuel and lubrication for the two-cycle piston engine and lubrication for the chain and bar. Two-cycle engines lack a separate engine oil system. Instead, these small motors run on a mixture of gasoline and oil. The oil in the gas lubricates the piston and prevents scoring of the piston and the piston chamber walls. Two-cycle engines don't depend on an oil reservoir for engine lubrication, so the machines run equally well in any position.
  
  

Bar Lubrication

• The oil tank on a chainsaw holds special lubricating oil for the bar, not the motor. Bar oil's higher viscosity, compared to motor oil, makes the lubricant stick to the bar and chain even at high operating speeds. Air pressure builds in the tank when the motor runs and automatically expresses bar oil at a measured rate. If owners fill both tanks as fuel runs low, the bar never lacks lubricating oil.
  
  

Damage

• Using gasoline, as a substitute for bar oil in the oil chamber, reduces the lubrication of the bar and chain. Without the right lubrication, the moving chain overheats the chainsaw bar. Links on the chain also overheat and freeze up or break. Broken chains could snap back and seriously injure the saw operator. Overheated chains and bars lose temper, wear quickly and cut poorly. Gasoline evaporates quickly on the hot metal parts and offers very little protective lubrication.
  
  

Dangers

• Normally, chainsaws throw small amounts of lubricating oil off the chain during use. With gasoline in the oil chamber, gas flows through the system at a much faster rate and flies off the bar. The spilled gas soaks the work area and creates highly explosive fumes. A spark from the overheating chain and bar or the chainsaw exhaust could trigger an explosion. Gasoline in the bar oil chamber could set the saw, the operator and the work area ablaze.