Thermostat housing swap

alldodge

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Can I keep my original hoses swapping over to a one piece Sierra 18-1989 t-stat housing from the original cast iron Merc housing 87290A4?

Sierra
sie18-1989.jpg

http://www.boatersland.com/images/img/sie18-1989.jpg

Merc
GLM-13230-2T.jpg

http://www.boatpartheadquarters.com/...M-13230-2T.jpg

IMO no, you would need to replace the exhaust manifolds and elbows as well. Here is your design
1987 GM350 design 1.png

Here is the later design
1987 GM350 design 3.png
 
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alldodge

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Manifolds? Why?

The newer housing looks to not use water hoses to the risers. I'm thinking would just plug the risers.

Old style
14401d1182643117-mercruiser-260-emitting-steam-boat-002.jpg

http://www.boatdesign.net/forums/at...17-mercruiser-260-emitting-steam-boat-002.jpg
New-GM-7.4-Inboard-Complete.jpg

New style

http://daddyosmarine.com/home/wp-content/uploads/2012/06/New-GM-7.4-Inboard-Complete.jpg

Then your correct you probably don't have to replace your exhaust, only the gaskets going between manifolds and elbows. Didn't know for sure since no serial number was given. To verify we would need your engine serial number. There can also be a water pump issue but like before would need serial number to determine.
 

JaCrispy

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Eng# 0B733876

I just bought riser gaskets, 2 sides have large openings and 2 sides just have 2 small holes.
 

achris

More fish than mountain goat
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To properly do the conversion you also need to understand that you will be going from 'warm' manifolds to 'cold' manifolds. Once you understand that, and what that means, by all means go ahead and make the conversion. Just be sure you have 'full flow' gaskets between the manifolds and the elbows. And as long as each hose from the bottom of the manifolds reaches the correct port on the new thermostat housing, you can even reuse them, but if they don't you'll need to replace them too.

Chris....
 

alldodge

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Here is the service bulletin on stainless to cast iron elbows, you shouldn't need it unless your elbows are in bad shape
http://www.mercruiserparts.com/bulletins/018/04//1999/EN_01.PDF

Appears it will work and you have the correct gasket (item 9 only two large holes)
http://www.mercruiserparts.com/Show...IFOLD+AND+EXHAUST+ELBOW(CAST+IRON+EXH.+ELBOW)

The elbow hoses would be removed and the other hoses would go to the bottom of the manifold. Just did some looking and it should work, only issue that may appear is keeping the block full of water. The older designed used the thermostat to keep water restricted to the block until the thermostat opened. The check valves in the exhaust elbows also helped keep everything filled. The alpha drive does not supply the same amount of water that the belt driven pump does on a bravo. So the only possible issue I can see is maybe some heat issues. If this turns out to be the case (not saying it will) may need to look into other options.

This pic is for illustration only, it's not yours but design issues are the similar

898 cooling.jpg
 
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