Hey guys! I have a super clean 1999 Islander 212 with the 454 MPI motor @ 475 hrs. Always stored on its trailer inside my garage out back of the house. Have always changed the oil every 50 hours or once per year if hours not met. I LOVE this boat and love the size, speed and look so I want to keep her going for as long as possible.

How do you know when to replace the exhaust manifolds? I have heard when they rust through it can cost you an engine. Current motor runs great and has no problems. Engine bay is spotless except for flakes of rust falling off the bottom sides of the exhaust manifolds especially towards the back of the engine (tired of vacuuming rust flakes out of bilge). If you look at the engine from the top you would never notice the rust it is all on the bottom of the manifolds down by the spark plugs. Should I spend $1k on putting new manifolds on her?

you can pressure test them to know for sure. do you run in salt or fresh water? that makes a big difference.

Only fresh water. Just the local Texas lakes.

If I take them off can I do a visual inspection to see how much material is left and tell maybe how much longer they will last?

I service some boats that are mid 80's thru mid 90's. Freshwater.Stay at docks while they are in the water for over 1/2 the year. Still have OE manifolds.
The other 1/2 they are winterized full of coolant.

So, I guess it depends on your water and luck ?

Ok funny you should mention that. I am wondering if because I store in a climate controlled garage (no antifreeze run through engine) that would have accelerated my rust. Never have filled the engine with antifreeze because she has always been in a heated garage!

I winterized this year on December 12th and went on my first ride of the spring on March 16th.

Actually,this is why I mentioned it. You are not alone with how you store.

I went through 2 sets in 500 hours. Some salt and some fresh usage. 2nd set cost me a motor.