DIAGNOSIS Bar oil is siphoning from the tank through the oil pump. This is almost always caused by a missing or damaged oil tank vent. The vent is a small one-way valve on the oil tank cap or body.
FIX Locate the oil tank vent. On this model, it is integrated into the oil filler cap assembly. Remove the cap. Clean the small vent hole in the cap with a thin wire. Blow compressed air through it from the inside. If oil still leaks, the entire oil cap assembly (part # 537210301) must be replaced.
IF THAT DIDN'T WORK The oil pump itself has failed and is stuck in the open position. This requires removing the side cover and clutch assembly to access the pump. Replace the entire oil pump assembly, part # 537210701. Ensure the oil feed line from the tank to the pump is securely connected.
HEADS UP Never store the saw on its side with oil in the tank. Always store it upright. Bar oil will degrade rubber and plastic, so clean any spilled oil off the saw's housing immediately.