My 373 vented loop does this. I've cleaned it and inspected it and can't find a problem. Guess I will replace it.As Doug said, volvo seal is the number 1 cause. You could also check the vented loop (air vent) too, especially if and most probably you will, have the "version" with the valve. It may need some cleaning/washing with fresh water for the valve to work properly.
The shaft seal replacement will require a haulout. The prop has to be pulled and the shaft removed, or a least pulled back a few inches. With luck, the rudder will not have to be dropped. The tail housing attachment flange will also have to be removed in order to remove the old shaft seal and replace it. If the prop shaft needs to be completely pulled, it would be a good time to replace the cutlass bearing as well.What are the steps involved in replacing the shaft seal? Tks
You will need to disconnect the shaft from the gear box, pull back the shaft a little bit (no need to remove the propeller; usually there's enough space), remove completely the shaft coupling and the key (keyed tapered bore coupling I guess), undo the two screws holding the volvo sheal and remove, grease the new unit a little bit, install the new unit using that plastic red colour "collar" so you don't harm it when sliding it if the shaft is not perfectly clean and shining, some more grease at the seal and install back everything. Theoretically, if you are brave and fast you can do it with the boat in the water. I am not that brave...What are the steps involved in replacing the shaft seal? Tks