I have a 580k backhoe that has a small crack on top of the main frame near the gear selection lever. The hydraulic tank is low and i still have oil running out of the crack with the engine running and the machine sitting still. Are these hydraulic tanks/frame under pressure all the time. I noticed that the fill cap has a vent release on the cap. Was wondering if there is a vent plugged or if the pressure in the tank is normal. Someone used jb weld to try and patch the hair line crack and it didnt work..so again are the hydraulic tanks normally under some pressure
They are designed to build a small amount of pressure as oil is moved in & out of tank & temperature rises, to assist in feeding the oil to the hydraulic pump. If the crack is big enough they will continue to leak sitting over night, even if the pressure has been released by removing the filler cap. The weight of the oil above the crack & gravity are simply doing their thing.