I have a VP D1-30 which now has 1,900 hours on it. I thoroughly maintain this engine
and it runs perfectly. When running at 2,400/2,500 RPM
my sailboat moves at about 6.5 knots and this is the speed I normally operate it at. At 1,300 hours I removed the exhaust elbow
and found it to be 50% blocked. I cleaned out the carbon/salt accumulation and reinstalled it. Recently, I removed the exhaust elbow
again and discovered that after 600 hours it is 25% blocked. Is this normal? Should I replace the exhaust elbow as the casting appears to be rusting from the inside (difficult to determine how much material has been eroded away)?