3.0L Raw Water Intake & Drain Port Questions

HeadAbove

Cadet
Joined
Jun 4, 2023
Messages
8
Hi All,

Mercruiser 3.0L (1A311803); Aftermarket closed cooling half-system; A1G2 drive.

I'm trying to simplify my current hoses, routings and drain process, mainly because the PO who installed the aftermarket closed cooling system left some of the superfluous OEM fittings in place. (I've read the installation instructions to validate this.) And I think these pieces left behind are confusing me. So, a couple of questions:

1) The raw water intake hose which runs from the transom to the aftermarket HE is a 2-piece hose with a "T" fitting in the middle. (Mercury p/n 32-862325.) The narrower, 24in long hose off the "T" routes down to another "T" fitting at the lower drain plug on the port side of the engine.
What is this hose for?
I was thinking maybe it's to hook-up a flush kit. Or maybe to allow the transom intake hose to drain with the rest of the sea water. But then I realized that the intake hose would drain naturally out of the transom whenever the sterndrive removed. So is the single purpose of this smaller hose to drain the intake hose whenever the sterndrive can't be removed from the boat?
I would really like to delete this "T" fitting from the raw water intake hose and just use a straight-through 1in hose coupler.

2) Again in the spirit of simplification, I want to remove what is left of the single-point drain system in my boat. I want to remove the handle bracket and the one remaining blue hose. (The other blue drain hose became obsolete with the closed cooling system.)
I will then replace the sea water quick drain/hose fittings with a stainless drain plug.
But I'm having trouble getting my head around which drain port is which...
...If there is sea water running through my exhaust manifold and coolant running through my cylinder block, why is the drain plug directly underneath the exhaust manifold now sealed-off (by a brass plug supplied in the closed cooling kit) and why do I get sea water out of the lower, block drain port?
In my mind, the port to drain the exhaust manifold of sea water should be the one right underneath the manifold and the block drain (coolant) would be the lower port on the block. But this appears to be the opposite of what I'm seeing.

Hopefully someone can tell me what I'm missing without making me feel too stupid.
Tks!
 

Grub54891

Admiral
Joined
Jun 17, 2012
Messages
6,073
How about some pictures of the setup. Haven't dealt with that style of cooling system on a 3.0 myself.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
49,560
full system or half system? you have to know this and understand this prior to making any changes.

half system: raw water comes in from drive, thru optional power steering cooler up to heat exchanger raw water inlet. raw water outlet is plumbed to manifold and exits. glycol inlet is plumbed to thermostat housing outlet. thermostat housing must be modified or replaced with simple (automotive style) water neck. glycol outlet is plumbed to motor water pump. fill line will be from bottom of purge tank to bottom of lower radiator hose. optional vent line will be from thermostat housing to purge tank.

full system: raw water comes in from the drive, thru optional power steering cooler, up to heat exchanger raw water inlet. raw water outlet is plumbed to riser elbow. a block-off gasket is used between the manifold and elbow. glycol inlet is plumbed to thermostat outlet after the thermostat. exhaust manifold coolant supply is plumbed to thermostat outlet BEFORE the thermostat. Exhaust manifold coolant return is plumbed to the thermostat housing after the thermostat, or teed into the heat exchanger glycol inlet. the glycol outlet is plumbed to the motor water pump. fill line will be from bottom of purge tank to bottom of lower radiator hose. optional vent line will be from thermostat housing to purge tank.
 

HeadAbove

Cadet
Joined
Jun 4, 2023
Messages
8
Thanks, Scott. Helpful detail.
I did understand the principles of both systems, I just couldn't reconcile those principles with what I thought I was seeing in my boat.
Turns out I completely misremembered the set-up and it wasn't until I could get into it today that I resolved most of my questions.

Mine is definitely a conventional half system... With the raw water manifold drain right where it should be and the block drain for coolant right where it should be.
Some pics attached.

But my first question still stands: What is the function of that narrower, OEM hose in my 3rd photo? This hose "T"s off the raw water intake hose at the top of the engine and plumbs down into another "T" at the manifold drain.
This is the fitting and hose I would like to delete and replace with a straight-through 1in OD nylon coupler in the raw water intake.
I would also like to replace the plastic fittings at the manifold drain port with a single, "wing nut" style stainless plug. (Which I assume will screw into the larger brass fitting which enters the manifold.)
 

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Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,439
Thanks, Scott. Helpful detail.
I did understand the principles of both systems, I just couldn't reconcile those principles with what I thought I was seeing in my boat.
Turns out I completely misremembered the set-up and it wasn't until I could get into it today that I resolved most of my questions.

Mine is definitely a conventional half system... With the raw water manifold drain right where it should be and the block drain for coolant right where it should be.
Some pics attached.

But my first question still stands: What is the function of that narrower, OEM hose in my 3rd photo? This hose "T"s off the raw water intake hose at the top of the engine and plumbs down into another "T" at the manifold drain.
This is the fitting and hose I would like to delete and replace with a straight-through 1in OD nylon coupler in the raw water intake.
I would also like to replace the plastic fittings at the manifold drain port with a single, "wing nut" style stainless plug. (Which I assume will screw into the larger brass fitting which enters the manifold.)
Would think the T will let air in the raw water hose so it drains back both ways ? Otherwise water would lay in there and freeze. Can only assume it is essentially a vacuum break. There is a name on the heat exchanger would think there tech dept can answer the question
 

HeadAbove

Cadet
Joined
Jun 4, 2023
Messages
8
Would think the T will let air in the raw water hose so it drains back both ways ? Otherwise water would lay in there and freeze. Can only assume it is essentially a vacuum break. There is a name on the heat exchanger would think there tech dept can answer the question

Thanks.
Yes, an air "admittance" vent is my best guess, too.
But as I remove my sterndrive at the end of every season and also disconnect the raw water intake at the HE, that hose has all the opportunity it needs to drain from both ends without the additional vent.

The installation instructions for this Seakamp half-system kit say to remove these OEM fittings and replace with their supplied, straight-through 1in coupler. The PO/installer chose not to do that step for some reason.

In any case, I'm going to remove both "T" fittings and that smaller hose. If it causes any issues I can reinstall the OEM fittings.

Thanks again, Scott D. & Scott06, for the inputs.
 

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Scott06

Admiral
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Apr 20, 2014
Messages
6,439
Thanks.
Yes, an air "admittance" vent is my best guess, too.
But as I remove my sterndrive at the end of every season and also disconnect the raw water intake at the HE, that hose has all the opportunity it needs to drain from both ends without the additional vent.

The installation instructions for this Seakamp half-system kit say to remove these OEM fittings and replace with their supplied, straight-through 1in coupler. The PO/installer chose not to do that step for some reason.

In any case, I'm going to remove both "T" fittings and that smaller hose. If it causes any issues I can reinstall the OEM fittings.

Thanks again, Scott D. & Scott06, for the inputs.
Oh I thought they were part of the kit , then by all means remove them
 

HeadAbove

Cadet
Joined
Jun 4, 2023
Messages
8
Oh I thought they were part of the kit , then by all means remove them

Yeah, I'm feeling more confident about doing that now đź‘Ť.

I did figure out that I'll need an additional bushing after I remove the plastic "T" from the manifold drain. (Mercury p/n 22-862557).
All good.
 
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