What are the two purple faucet-like knobs on sea water pumps

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What are the two purple faucet-like knobs on sea water pumps

Postby RufusNapkin » Mon Dec 03, 2018 7:37 pm

What do they do and how do you know if they're open or closed? Can damage occur if their position is opposite of what it should be? - I am about to replace a water pressure sensor and they are right there, on the sea water pump enclosure.
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Re: What are the two purple faucet-like knobs on sea water p

Postby SGilbert » Mon Dec 03, 2018 7:55 pm

Those look like standard MerCruiser drain plugs. Used while winterizing.
Unscrew one of them to verify. (Do not loose the O ring)
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Re: What are the two purple faucet-like knobs on sea water p

Postby stitchsc » Mon Dec 03, 2018 8:32 pm

Yeppers
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Re: What are the two purple faucet-like knobs on sea water p

Postby RufusNapkin » Mon Dec 03, 2018 10:01 pm

SGilbert wrote:Those look like standard MerCruiser drain plugs. Used while winterizing.
Unscrew one of them to verify. (Do not loose the O ring)


My concern is, What if someone inadvertently closed them when they should be open, or open them when they should be closed - while the boat is being used?

The logic of how they function is elusive.
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Re: What are the two purple faucet-like knobs on sea water p

Postby Chris_in_Texas » Mon Dec 03, 2018 11:02 pm

They are drain plugs not valves. They unscrew out of the manifold to drain the water.
Thanks, Chris

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Re: What are the two purple faucet-like knobs on sea water p

Postby RufusNapkin » Tue Dec 04, 2018 1:12 am

Chris_in_Texas wrote:They are drain plugs not valves. They unscrew out of the manifold to drain the water.

So if no water is coming out they're as they should be?
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Re: What are the two purple faucet-like knobs on sea water p

Postby gofast24 » Tue Dec 04, 2018 11:37 am

RufusNapkin wrote:
Chris_in_Texas wrote:They are drain plugs not valves. They unscrew out of the manifold to drain the water.

So if no water is coming out they're as they should be?

Agree with Chris, they are drain plugs, not on/off valves. Whether water is coming out when you remove them depends if the boat has been pulled out of the water for winter and the water from the sea/to the pump and up to the engine thru the sea water pump has self drained or not. If no water comes out and the boat has been out of the water for several days or weeks just leave them partially open or totally out but dont loose them and put a note on your helm indicating "sea water pump plugs removed, do not start engine! If the boat is still in the water do not remove them, especially the one that is the pump inlet to the sea!
Not having to pull our boat over winter wish I had these sea water pump drain plugs on my last 4 boats! Always had to pull the hoses from the outdrive pump to and from the engine jacket water heat exchanger as well as engine oil cooler to make sure no sea water left in the cooling system! Also, still wonder if u have to or should drain the sea water cooled exhaust manifolds/risers to make sure no fresh water in the system? For the last 4 boat I had always did that as well, dont know how the Merc sea water drain plugs work regarding the cooled exhaust manifolds/risers or possibly you have a two circuit fresh water cooled engine?
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Re: What are the two purple faucet-like knobs on sea water p

Postby RufusNapkin » Wed Dec 05, 2018 3:07 pm

gofast24 wrote:
RufusNapkin wrote:
Chris_in_Texas wrote:They are drain plugs not valves. They unscrew out of the manifold to drain the water.

So if no water is coming out they're as they should be?

Agree with Chris, they are drain plugs, not on/off valves. Whether water is coming out when you remove them depends if the boat has been pulled out of the water for winter and the water from the sea/to the pump and up to the engine thru the sea water pump has self drained or not. If no water comes out and the boat has been out of the water for several days or weeks just leave them partially open or totally out but dont loose them and put a note on your helm indicating "sea water pump plugs removed, do not start engine! If the boat is still in the water do not remove them, especially the one that is the pump inlet to the sea!
Not having to pull our boat over winter wish I had these sea water pump drain plugs on my last 4 boats! Always had to pull the hoses from the outdrive pump to and from the engine jacket water heat exchanger as well as engine oil cooler to make sure no sea water left in the cooling system! Also, still wonder if u have to or should drain the sea water cooled exhaust manifolds/risers to make sure no fresh water in the system? For the last 4 boat I had always did that as well, dont know how the Merc sea water drain plugs work regarding the cooled exhaust manifolds/risers or possibly you have a two circuit fresh water cooled engine?

First thought that comes to mind is what if these were faucets, same everything, except the plugs don't detach. This would be like an extra place to periodically clear those water passages of any junk before it enters the engine? While the boat is in the water.
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Re: What are the two purple faucet-like knobs on sea water p

Postby SGilbert » Wed Dec 05, 2018 4:17 pm

You are WAY over thinking this. Do not open in the water. They are not faucets, they are drain plugs.
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Re: What are the two purple faucet-like knobs on sea water p

Postby Chris_in_Texas » Wed Dec 05, 2018 5:45 pm

I wouldn't take them out in the water. You could but if one was brittle and broke while unscrewing it. You have the wooden or foam plugs right? :mrgreen:
Thanks, Chris

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Re: What are the two purple faucet-like knobs on sea water p

Postby Bt Doctur » Thu Dec 06, 2018 8:58 am

Why they would add a sensor is a mystery unless its so you have to buy the $80 part when simply watching your engine temp gauge will do the same thing.
To tell you when you need impeller service. Currently working on a resistor setup to bypass that funky gauge
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Re: What are the two purple faucet-like knobs on sea water p

Postby gofast24 » Thu Dec 06, 2018 12:10 pm

Bt Doctur wrote:Why they would add a sensor is a mystery unless its so you have to buy the $80 part when simply watching your engine temp gauge will do the same thing.
To tell you when you need impeller service. Currently working on a resistor setup to bypass that funky gauge


I dont see any sensors in the picture? How did we get to $80 sensors needing to be replaced unless I missed a post here? Also, assume there would be sea water strainers upstream to catch any junk and not make it all the way to the sea water pump inlet/outlet? But if there was a flow sensor with either a gage at the helm or alarm (probably a low sea water pressure sending unit) that would be much preferable to waiting for your engine cooling system temp gage/alarm to go off telling you you no longer have sufficient sea water flow?
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