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

Postby RufusNapkin » Thu Dec 20, 2018 12:18 am

I was replacing the fuel pump today. There was one of those blue knobs close to the pump (water pump area) so intuitively I tightened (clockwise) it. But it didn’t look like it moved at all. But suddenly when I fired it up white exhaust appeared and is not going away. It never had this before. Water flow from exhaust looked normal. Also briefly, a one-time two-beep. The temp gauge went somewhat higher than usual on that engine also. Then it almost stabilized. All this at park and increasing throttle for about 45 seconds to1500.

I could have pinched a hose going into the sea water pump? Everything was normal before.

I still don’t understand those blue knobs. Can someone please explain it to me like I’m an idiot? Seriously. Are they PLUGS?! Maybe the simplest question is, Clockwise or anti clockwise during normal engine operation?
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Re: What are the two purple faucet-like knobs on sea water p

Postby Chris_in_Texas » Thu Dec 20, 2018 12:58 am

They should be drain plugs. If you order them that is what they are called. If they aren't closed either one will spill water all over (output side) or the other side will allow air in and burn up the impeller when its running. Otherwise the inlet side should spill water all over when its out as the pump should be below the water line.

https://www.marineengine.com/parts/merc ... water-pump

Plug kit, blue, drain

Almost sounds like the way the military does it... :mrgreen:
Thanks, Chris

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

Postby RufusNapkin » Thu Dec 20, 2018 1:27 am

Chris_in_Texas wrote:They should be drain plugs. If you order them that is what they are called. If they aren't closed either one will spill water all over (output side) or the other side will allow air in and burn up the impeller when its running. Otherwise the inlet side should spill water all over when its out as the pump should be below the water line.

https://www.marineengine.com/parts/merc ... water-pump

Plug kit, blue, drain

Almost sounds like the way the military does it... :mrgreen:


So just make sure they are "both clockwise" tight (while the pump is oriented same as in the diagram)?

"burn up the impeller while it's running". That is what I want to avoid. Tomorrow I will look down there again to see if I did something out of place.
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Re: What are the two purple faucet-like knobs on sea water p

Postby SGilbert » Thu Dec 20, 2018 8:58 am

Each plug has an O ring on it. Are you sure they are there?
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Re: What are the two purple faucet-like knobs on sea water p

Postby RufusNapkin » Thu Dec 20, 2018 11:54 am

SGilbert wrote:Each plug has an O ring on it. Are you sure they are there?

Wouldn’t there be a leak of some sort if they were missing?
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Re: What are the two purple faucet-like knobs on sea water p

Postby gofast24 » Thu Dec 20, 2018 12:05 pm

Yes, but if not running the engines the inlet or discharge port of the pump wouldnt have any more pressure then sea water "head" pressure (maybe a foot or tow). Try to observe the two valves when the engine is running, specially the discharge port to confirm if the o rings are ther or not. Could also just remove the two plugs and see if there are "O" rings on them dont do it when the engine is running, just when engines off!?
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Re: What are the two purple faucet-like knobs on sea water p

Postby Chris_in_Texas » Thu Dec 20, 2018 7:58 pm

If an o-ring would be missing on the inlet there could be air being sucked in. That is why the "engine flush" on the VP engines, you have to make sure that fitting is tight and not leaking, as it won't "leak water" but will suck air and cause over heating issues.
Thanks, Chris

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

Postby RufusNapkin » Fri Dec 21, 2018 12:37 am

Chris_in_Texas wrote:If an o-ring would be missing on the inlet there could be air being sucked in. That is why the "engine flush" on the VP engines, you have to make sure that fitting is tight and not leaking, as it won't "leak water" but will suck air and cause over heating issues.


Can these drain plugs be used to clear debris? Are those water passages susceptible to debris that could in turn either enter the sea water pump or heat exchanger?
I basically took the boat out, drove it for a couple of hours, all gauges read normal. Except at the end of the drive as I was reducing throttle from 3,500 to around 2,500 I got the infamous 2 beeps each two minutes. Even thought I did go from 3,000+RPM to under 2,500 several times during the two hours, there were no beeps. Just when I was going back to the docks.

Both water pressure sensors are new (Sierra); IACs seem to work fine at idle also.

I read somewhere about needing to clean the heat exchanger for this, and another, even more interesting solution, raw water pickup hose (transom intake). Corroded fitting reducing inside diameter of the hose to 1/4" at the fitting, or something like that. Not sure if this applies to inboards, howeverr. I did notice today that one of the seacocks on one of the raw water strainers, when closed, still allows water to seep through. Time to replace.
Last edited by RufusNapkin on Fri Dec 21, 2018 12:45 am, edited 2 times in total.
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