1968 Mercury 100hp Water from upper exhaust openings

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BeefCakes

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Joined
May 22, 2020
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4
I recently fired up this 68 100hp Mercury engine, discovered the tell tail was plugged....the engine was still cold so it was pumping I just didn't know how good (it was on the muffs). Decided to go ahead and put a new pump in and I think I may have messed something up for as the video shows exhaust and water are shooting out the ports under the power head. I did not remove the exhaust tube or did it even move when I pulled the lower unit and don't recall if it was doing this prior to the new pump, as mentioned I only had the muffs on for a short period before I changed the pump. I have 65 100 hp engine also and I don't recall it doing this. The question is, did I mess something up, miss a gasket or is this normal. I know there is an exhaust gasket on the bottom of the tube, it seemed good so I left it alone. I'm not very savvy with outboards so I really don't know, was hoping one of you would set me straight.
This is a 1968 1000ss
 

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Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,669
When the engine is running and the boat isn't moving, the depth of the water at the engine is "back pressure" on the engine when it doesn't need any. The/those hole(s) at the rear of the mid section, near the top are called "Exhaust Relief Ports" and are there to relieve exhaust pressure. Since the cooling water exits the power head along with exhaust, some water will come out at idle. When the boat is running and water no longer touches the transom, there is actually a suction at the prop and the relief ports aren't needed. Buttt:

I had a 125 Johnson which I used to water ski behind. At idle there was only a sputtiering of water along with the gasses, but when I was on skis and we were running in the wide open throttle range, the ports were full flow....I just found that interesting. I guess since that was the path of least resistance and the volume of water was large some of it chose to exit a goodly amount there.
 
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