How long do the cast iron manifolds last in saltwater. My boat has closed cooling but the manifolds are raw water cooled. The manifolds have some rust stains driping down from the risers and alot of rust where the manifolds bolt to the engine. I flush them after every use with water and saltaway for 10 minutes and I have 200 hrs/ 1 year on the boat. Is it time for new ones already?
200 hrs you should be fine. if you are worried about it order new gaskets from skidim break them apart and look at it. i took mine apart decked the two pieces with a beltsander. and reinstalled the new gaskets. good as new. if water is leaking to the outside then you can bet its leaking to the inside of the head, and that aint good at all!
I agree with 882001, you should definitely break them apart and sooner rather than later. Pray that the bolts holding them together are stainless steel or another noncorrosive metal. When I tried to get my risers and manifolds apart I broke a number of bolts. (Take note thought that my boat was 17 years old.) (But it's also never seen salt water.) Hopefully you just have to put new gaskets on every few years rather than whole manifold/riser replacements. Best of luck!!!
You should get about 7 years out of them. also it is good practice to change the gaskets annually and drag a flat file across them when changing the gaskets. This will keep the surfaces flat and clean in the event you have some salt water seapage under the gasket.
Yes thats what I do. As far as the rusting near the block that is kinda strange. Are you sure it is not from the leak where your riser bolts onto your manifolds? Like the leak could be running down the manifold adn running along where they bolt to the block. I had a similar thing 2 years ago, I couldn't figure out why my starter kept dying and it turned out I had a leak fron my riser / manifold that was running down the side facing the engine and right into my starter.