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My boat has what appear to be the original Mercruiser 454s, but the exhaust manifolds and risers (see attached picture) don't look like the ones in the pictures that I have seen on line. Is this a standard setup? (This is my first attempt to attach a pictures so I apologize if it does not work.)

http://www.ipernity.com/doc/307687/45982844

thanks,

They are the older mercruiser log style manifolds. What's going on with your left side valve cover/oil fill?

Yes. There is one on each side. They fit in the hole like a stopper.

Peter

John is correct these are the old style manifolds and risers. Nothing wrong in keeping them. Change the risers every 7 to 8 years could be sooner depending on where you keep the boat. Ours is always docked in brackish water. Most we ever got out of the risers was 8 years. If one goes change all of them.

Are the risers fresh water cooled?

Peter

The risers have fresh water running through them but the issue is on the exhaust side. You have hot exhaust gas and sea water coming out the risers. The Sea Water is the enemy and causes them to fail. Failure usually leads to water in a cylinder and or oil.

Since we kept the boat docked in an area with Brackish water, they would flush out some and we would get 7 to 8 years out of them. We would automatically change them every 7 years just to be safe. The one time we had a failure it was while the boat was layed up for the winter. I guess the riser rusted through either just before lay up or over the winter and when we started her in the spring, we found antifreeze in one of the cylinders.

Just keep prevention in mind. I would say if you were strictly salt water not brackish and you don't flush the engines with Fresh water at teh end of a day, then I would change them every 5 years. Others on here might have other thoughts.