Good afternoon!
I have a problem with stern tube. Today checked the header tank and it was overflowed. Yesterdey everything was ok. At the moment the oil is staying in one level but higher than it was aproximetly 10 cm higher (Header tank is full).
Stern tube is naturaly lubricated. No pumps.
Ship is 25 m trawler.
Any advice would be appriciated.
Thanks!

There should be a Hydrostatic pressure balance between the water outside and the oil inside, because Sea Water is more dense than oil the stern tube header tank is always higher then the Sea Water outside, in proportion to the different SGs.
Has the Draught aft increased ? That might cause Sea water to pass in through the Stern Tube Seals and increase the level of the header tank making it overflow.
BP

no experience working on a trawler. Does the stern tube have an arrangement to check void space between the sea water and oil seal. If you do...draw a sample and you will know if your seal has compromised. Check the vent is clear.