Old Mastercraft Question- need help

I have an '89 Prostar 190 that I bought three years ago. It was used up until that time in brackish water, so the engine is quite rusty. It runs great, but I have had to replace the exhaust manifolds because they pretty much rusted out. I am worried that the block may be in the same condition...when I drain it in the fall, rust drains out with the water from the block. I am trying to decide if I should get rid of it now before there are bigger problems, but I didn't want to have to buy a new one for 3 more years. Has any one had this problem with exhaust manifolds, and if so, did a problem with the block or other major components follow shortly after? Any advice would be greatly appreciated.

Haven't had this problem, but my understanding is the inner walls are much thinner in the manifolds than the block. IOW, a block could go thru 2 or 3 sets of manifolds, and probably need a rebuild before rusting out. How did you know the manifolds needed replacing? Did they leak externally, or did the motor hydrolock?

They leaked externally...I heard the exhaust sounding much different all of a sudden, and I could feel exhaust coming out the bottom of the starboard manifold.

When you say need a rebuild, what did you mean would need to be rebuilt?

Thanks for the help!

Doug- by rebuild I think Trace means you most likely will have to replace things such as piston rings-crank bearings-pushrods etc well before worrying about the block rusting thru.

Ding!

Strange things sometimes happen with boats. A friends boat ran in the delta for 2000+ hours, the block was full of mud when it came to rebuild time. These 351 blocks/heads are readily available for reasonable prices. I would say run it until it rusts through then fix it. No sense in getting worried until it's time. Exhaust manifolds tend to go first from my experience, I would not judge the block based on the manifolds.

I used my 87 for all its life in saltwater with no issues on the block and we have a 22 year old MC here which has done all its life in salt, again the block is fine. This one is never flushed either as it spends 8 months a year moored up.

If you want to run it till the block rusts out you'll be waiting till you an old man!

Mine was run in brackish water also. the heads started leaking water, through a crack that had rusted out. New heads, and its back running strong

For the Mike whose was run in brackish water. How old was your boat, and how big a repair was it to put new heads in? Did your manifolds go first and if so, how long before. Thanks.