OK, so i currently own a 1998 Baja Hammer with a 454 Mercruiser I/O. Ever since we got the boat, I've been having problems with it. 2 Years after we got the boat, the exhaust manifolds cracked, so we got that repaired under warranty, replacing them with a higher grade of manifolds. 2 years after THAT, they cracked again, so we got it repaired, AGAIN. And now, they cracked AGAIN! I winterize the engine BY THE MANUAL so i don't know how it's possible that every 2 years, we have the same problem with this engine. I don't really want to spend money to fix this problem again, because it's probably just going to break in another 2 years. And sinking 10-15 grand into an engine isn't really my idea of a fair compromise either. I don't know what to do. Any answers would be greatly appreciated.

I don't know what the manual says, but you're not doing something right! I've never cracked a manifold and my boat is kept in cold northern michigan. I drain the manifolds using the drains on the back of the manifolds then I fill the cooling system with RV anti-freeze.

I have a new to me boat with bbc, found a couple sights on line that said a bbc would hold 2 gallons of anti-freeze to winterize. I ended up putting 4 & 1/2 gallons in. Sounds like your not getting all the water out. But just happening 2 years apart sounds funny

I don't know how you're winterizing your blocks/manifolds, but if this is only happening after winterizing then I'd say you're doing something wrong. I basically do the same thing endevour does and I've never had a problem either.

The easiest way to winterize your blocks, IMO, is by removing your thermostats, putting muffs on your outdrives (I'm assuming you have bravos) and connecting the muffs with a garden hose to a modified 5 gallon bucket that is full of antifreeze. That way antifreeze cycles through the whole system, and the best part is... you're done in about 20 minutes....

The BBC holds about 2 gallons itself... The manifolds hold about a gallon each, if you have the old style cast iron manifolds...

Stock exhaust manifolds won't crack in 2 years unless they are either badly overheated or the water in them freezes.

sorry, haven't been checkin this post
i remove all the plugs from the block, and fill the block with antifreeze through the thermostat housing. i also remove the plugs from the risers and fill them with antifreeze too. i use the purple colored antifreeze too...so i don't know what i could be doing wrong.
and sinking 2 grand into the same problem every 2 years doesn't seem right to me.

I'm not sure what motor plugs you have (I just have drains on the manifolds), but IMO its much easier to winterize through the drives so you know the antifreeze cycles through everything. I always drain the antifreeze out of the manifolds, but I mainly do that to run w/e anitfreeze that comes out of the manifolds through the bilge pump to make sure that's good too.

Depending on where you run your boat(river or lake), You need to pull out the lower block drains to get the sand out of the block. If you don't do this the water that is in the sand will freeze!!! Drain manifolds and block and run 1 gal. through with the block plugs only removed, Then put block drains back in and run 5 gal. through..Leave all the anti freeze in the system. What are you saying by "purple"? Are you saying you use -100 mercury blue?

By purple, we (my son and I) mean the stuff you get at West Marine. They sell pink, purple or green colored antifreeze. The purple stuff is in the middle of protection (between pink, which has least protection, and green). Also, I pull ALL the plugs, even the hard to get at plugs for the lower part of the engine. I usually poke it with a piece of wire or very small screw driver to break up the gunk until the water drains freely. And for the risers, I pull the hoses, drain the water, and pour in antifreeze through the hoses that supply water to them, until anti-freeze pours out the exhaust. And normally, after I am done, I have used about 5 gallons, give or take.