Our boat is already 20 years old. It has Volvo MD2030 engines, and in the last years I have been reading more and more posts about older Volvo engines and problems that seem to originate from corrosion. Coolant disappearing, rusty coolant, leaks.
The MD2030 and many other marine engines has a freshwater and a saltwater cooling system. They are supposed to be separated. But with wear and corrosion there are possibilities that the saltwater can enter the freshwater system. The freshwater coolant can also find disastrous ways as a result of corrosion. The latter happened to us this summer.
We found ourselves in a small island harbour with hydraulic lock in the port engine. Could not be turned. Water in the cylinders was the first thought, and it was correct. All 3 were full of coolant. But where did it come from? The heat exchanger housing had been off a couple of years ago, looked OK, so a cracked engine top was suspected. After dismounting it nothing wrong was found. Luckily, via some social network groups I was steered to inspect the heat exchanger housing thoroughly. A tiny hole was found in the exhaust area. Probing it, the edges fell apart, and the hole was suddenly big. Corrosion had eaten the area.