I have a 2007 4.3L Mercruiser that had water intrusion due to the block rusting through from the cooling chamber to the oil chamber. The motor has never seen salt water, only fresh water lakes and it has less than 200 total hours on it. Each winter, I drain the water out of the motor through 5 drain plugs that drain both slides of the block along with the exhaust manifolds and water pump. Over the course of the winter, I hook up the hose with muffs to the water intake ports and start the motor about every 6 weeks to keep everything moving. Then, after the motor cools, I drain the water again as mentioned above. This February I started it and as usual, it ran great. I let it idle about 30 minutes and when I came back to shut it off, there was a yellow-white foam all over the engine. At that point, the engine was still running good. After inspecting the engine, I realized I had a serious water intrusion problem. Several weeks ago, I pulled the engine and tore it down expecting to find a problem with the intake manifold gasket or head gasket but all those were in good shape. What I did find was that the water chamber around the piston cylinders has severe rust issues and the metal had flaked off to the point that it breached the water chamber and water spilled into the oil chamber. What I'd like to know is if anyone else has experienced this problem? it seems to me that the block should have lasted a whole lot longer than 8 years before it rusted through.
