I already isolated the water heat exchanger. Still same.
getting the salt water result I checked the freeze point of the coolant versus the sea water. What was in the heat exchanger had the same freezing point as the ocean so i tried a drop. Definitely salt water
i did pressure checkes on every single tube in the heat ex. All good! Its now back in the engine. i used a high torque on the seals and also added some sealant.
will see over the coming weeks if it’s fixed.
SN 119 / Cascais, Portugal