Nanni N60 Diesel engine corrosion

[Barneyj]

I recently fitted a new Nanni N60 Diesel engine into my steel monohull yacht. After 8 hours of engine run time I discovered a spot of external corrosion of about one square centimetre on the raw water elbow very close to the raw water pencil anode. The anode was slightly wasted. The elbow casting was replaced with a new one and today after a further 20 hours of engine run time the new casting has corroded in almost the same spot with no wasting of the pencil anode. It has been suggested that electrolysis may be the culprit but wouldn't the anode be wasted completely before the casting began to corrode? Any ideas!

 

[oldsaltoz]

If it's cast iron it may be a common fault in manufacture, other that I agree if it was electrolysis the anode would be wasted.

Looking forward to other replies on this one.

Good luck and fair winds.