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    Small hole warm water exit lower drive unit opposite drain plug.

    Thanks for replying. What is the purpose of that hole? It’s coming out at pressure but everything else seems to be working perfectly. Lots of water out of the elbows boot area. Engine water system pressure is good.
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    Small hole warm water exit lower drive unit opposite drain plug.

    On the opposite side( right hand if looking towards the bow ) there is a small pencil diameter hole that is jetting out warm water when the engine running. My stern drive is 1 generation Alpha 1975 233hp 351 Ford Mercruiser (Cleveland I think) I’ve never noticed water coming out of there before...
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    140 or 160 thermostat. Does 20 degrees make a difference?

    Running a 140 thermostat on 1975 233hp 351cu Ford mercruiser when the suggested thermostat is 160. I’ve not noticed anything wrong with the engine’s performance but after cruising the temperature goes passed 140 to 160 plus but goes back down quickly to 140 after slowing down. Is there anything...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    After much deliberation and consternation the end result of an all out trial with removal of the block off plates was positive. Overall the manifolds ran warm but not hot and the engine about 140 due to the thermostat which should be 160 but what’s 20 degrees. The waters near Montreal in Canada...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    actually there will be! for those who may be interested in the end result and not irritated by it. your experience seems to be without doubt but mine isn’t, there are strange things at play here and i’m trying to figure it out. thanks for your reply
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    So the end result of the water test on my exhaust cooling system is this: boat was tilted up as if in bow up attitude and I ran the engine at 1000 rpm disconnected a return tube from the manifold and there was a lot of pressured water returning to the thermostat housing and all lot of water...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    I forgot to mention. When the boat came back from the mechanic only one side had been done which was the side with the burnt riser bellow so the other side still had the plate and when I ran the engine it was obvious the side that still had the plate heated faster and was significantly hotter.
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Sorry Chris. I meant to say a disconnected front manifold tube.
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Do think if I turn on the engine for a few seconds to see if water makes it’s way through the manifolds to the exit tubes at the front of the manifolds that go back to the thermostat. Yesterday I could feel warm water making its way through but how much I couldn’t determine
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Here’s another one Chris. Thanks again for your feedback. Maybe a call to Fond du Lac in Wisconsin May clear things up. That plate almost seems to be a modification of sorts and not the original design. My manifolds have circulation channels that are blocked off by those plates.
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Okay. I’m still wondering! Take a look at this schematic carefully. It’s still very baffling. It almost looks like those plates removed would bring more water through the manifolds.
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    thanks for responding. wouldn’t my manifolds get hot? they were the coolest i have ever felt them after 10 minutes at 1200 rpm. i appreciate your drawing but i still think a careful trial run to see what happens. thanks again.
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    left y exhaust ( helm side)hotter than right

    so i’ve been in a conundrum of exhaust cooling system advice and now “here’s the deal “ to paraphrase President Biden! both “blocking plates” from the manifold to heat risers in a 1975 351cu 233 Ford Mercruiser have been removed with a substantial increase in water flow out the exterior stern...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    that’s my engine! exactly! i will get to the bottom of this eventually and determine wether or not these block off plates actually serve a purpose. thanks for responding and sharing your photo.
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    i’m going to put magnetic thermostats on both risers and monitor the heat as we drive around the lake slowly as to not build up too much heat and see what happens. thanks for the insight
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    such an old engine with some mysteries, i don’t expect mechanics to know every aspect of every engine that’s out there, this is something i’ll investigate carefully to see what happens. i did discover some tubing that was reversed to the manifold which i corrected but wether that was the cause...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Why design passage ways for water at the end of the manifolds to the risers then block them off? Unless this system is also used for the mixed rawwater /coolant systems. Who knows?
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Hello again Alldodge. Here’s another diagram of my boat’s manifold system
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    “Closed cool” you mean dual raw water/ coolant systems. Mine is simply a fresh water system The inserted diagram is exactly my engine. No oil cooling,no transmission,etc. Straight from the lake cooling system. As you can well see those block off plates are in the design but the mechanic states...
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    1975 351cu 233hp Mercruiser, riser block off plates or not?

    Thanks Chris. This diagram is a bit confusing since my engine is a freshwater open system with no transmission or oil cooling. It’s a 1975 351ci 233hp Ford 2 barrel.
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