Mercruiser 8.1L engines with aluminum exhaust manifolds

[Big Daddy]

Has anyone had any problems with aluminum exhaust manifolds on 8.1L Mercruiser engines? I recently stumbled onto an online forum for Sea Ray owners with this issue. Obviously, the problem is much worse for boats used and kept in salt water. Apparently, due the extent of this problem, Mercruiser has had a "secret warranty" to replace these manifolds, but only when the owner complains. In other words, it's not been a publicized recall. Sometimes they corrode through the outer wall, so you get water leaking into your bilge -- messy, but not catastrophic. In other cases, they corrode through the inner wall, so water gets into the engine and causes a major failure, just like any other failed exhaust manifold.

I have a 2005 Maxum 3700SY with these engines with aluminum manifolds. I run in the Chesapeake bay, mostly in the north Bay, where the salinity is much lower, but we do periodically cruise down to the south of the Bay where the salinity is much higher, basically the same as sea water. So far, no problems with the manifolds, but I don't want any surprises.

[pascavone]

leaking manifolds is hardly a secret.....

since your boat is 8 years old, I'd replace your manifolds re guard less.

[Big Daddy]

True, leaking manifolds have always been a problem, especially in salt water, but Merc has never before had to offer a "secret" or any other kind of warranty on them. With the aluminum, the problem has been much worse -- hence the "secret" warranaty. But OSCO and the other aftermarket vendors don't yet have a replacement part, even in cast iron, so you're stuck with getting them from Mercruiser. List at abot $633 each, for manifold only, no riser, so you're looking at over $2500 to replace them all. I'll pursue the warranty with Merc.

[pascavone]

dose your boat have above the water line exhaust and the new catalytic converters?