Why Do Chainsaws Leak Bar Oil?

Having a chainsaw that leaks oil will not only create mess, but it can also impact your chainsaw’s performance. There are some simple steps that can reduce oil leaking from the chainsaw.

 Forester refueling MS 881 in the forest

Why is lubrication important?

Lubrication of the chain and bar on your chainsaw plays a vital role in promoting longevity in the chain.

All chainsaws have an oil tank which is designed to store special oil until it’s pumped through to the guide bar by the oil pump. A chainsaws chain can go through a variety of loads, but without sufficient lubrication, it runs the risk of heating up excessively which could cause irrepairable damage to the cutting attachment.

What causes a chainsaw to leak oil?

As the oil is pumped from the tank through to the guide bar, air begins to replace the space where the oil was previously stored. If there isn’t proper ventilation of the oil tank, a vacuum can occur and reduce the flow of oil to the guide bar. Correctly venting your chainsaws oil tank will allow air into the tank, and avoid a vacuum from occurring. 

There are a number of factors that contribute to why a chainsaw leaks oil. STIHL chainsaws use a one-way valve oil tank breathing system. This system allows air into the tank whilst the chainsaw is in use, without leaking oil onto the operator. However, in some atmospheric conditions the oil may be forced out of the tank through the oil pump while the chainsaw is in storage. This can be caused by normal variations in air pressure that occur due to changes in temperature throughout the day and night. This is particularly present in areas that experience more drastic changes in day/night temperature. 

For example; the drop in temperature overnight can cause the air and oil in the tank to contract and take up less space in the tank. The air is then drawn into the tank through the one-way valve breather to fill the space, and equalizes the pressure. As the temperature rises again during the day, the air and oil in the tank expands, because the valve is one-way, the only way for the pressure in the tank to equalize is for a small amount of oil to be forced out through the oil pump ports. This process can repeat each day and night cycle until, potentially in an extreme cases the tank may pump itself dry. 

 Check level of oil and petrol

How to correctly vent a chainsaws oil tank

STIHL chainsaws are designed to be operated at any angle or position without leaking oil. It’s important to note that oil tanks cannot simply vent into the atmosphere, as this could lead to the oil leaking onto the operator during use. To avoid your chainsaw from leaking oil whist in storage, the best solution is to drain the chainsaw of its bar oil and fuel mix and store the chainsaw empty.

If you need to keep oil in the tank, then the best way to vent your chainsaws oil tank is to lay the chainsaw on its side with the oil cap pointing upwards and open the cap slightly. This will reduce the pressure from building up in the oil tank during fluctuations in temperature. Just make sure you remember to tighten the filler cap again before the next time you used it.