raw water cooled in chesapeake bay?

My friend just bought a 1999 sea ray with 1999 mercruisers. It was on the cheasapeake and he brought it to lake erie. It is raw water cooled. I seem to remember reading something years ago about the fresh water swelling the rust in a raw water cooled saltwater boat. Has anyone ever heard that? Is it worth draining the block and filling it with diluted muriatic acid then flushing that out or will that do more harm than good.

the main concern is the manifolds and risers. on the Bay, 5 years is maximum life span. if you see rust at the connections, replace them. if they blow you can expect engine replacement. check the bellows and gear joints in the outdrive. depending on usage you may need new water pump impellers.

What i would do if this were my boat.

I have been in the exact situation.

I would replace the raw water pumps in the drive.

Check the billows.

Check the gimble bearings.

Remove check and or replace the elbows.

Check the flappers.

You could run salt away thru the engine before you check the elbows.

Elbows in fresh water could live 15 years or more.

Replace the t-stat.

Tune up done when ?

When i go to launch my boat after first buying it i go thru everything.

Oil is good in the engine, oil is good in the drive your good to go.

Agree.
No on the muriatic acid thing. The risk would be in not knowing what strength and/or duration to use, and not being able to neutralize it afterwards.
It may also damage the circ pump's ceramic seal.

And never take anyone's word regarding an impeller replacement.

As for the exhaust system, while it's best to replace these, the sea water transfer ports are what he'll want to look at.
These can often be cleaned free of rust scale, and made to flow well again.
The manifold to elbow mating surfaces can also be re-dressed on a machine shop surface sander.


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Any idea on the age of the manifolds and risers? The life span of a manifold/riser in the Chesapeake can be up to 20, not likley but they can last that long. Change them so you know for sure they won't cause a problem. The saltwater isin't the real culprit, air causes the most damage. You intoduce water and heat and then air gets in the system and it acceleratess the rust. That's why they fill the manifold with antifreeze in the winter,stops them from breaking and rusting in the winter. You don't say if the boat has straight drives or sterndrives.

Maybe 6 years in saltwater for the risers / elbows... manifold 15 - 20 years or more.