Mercruiser 5.7L Closed Cooling

[kbeckman]

I'm installing a Mercruiser closed cooling on a previous raw water cooled 5.7L V8, and need help with a couple hookups.

1. The hose from the top of the water pump goes where? It looks like the block, but I can't tell where.
2. There is a 90 degree elbow on the top of my thermostat housing right next to the bleeder valve. I think this is the bypass hose, but where does it go?

I almost think these 2 go together, but the parts manual shows 2 different elbows here, which has me confused.

 

[alldodge]

I'm installing a Mercruiser closed cooling on a previous raw water cooled 5.7L V8, and need help with a couple hookups.

1. The hose from the top of the water pump goes where? It looks like the block, but I can't tell where.
2. There is a 90 degree elbow on the top of my thermostat housing right next to the bleeder valve. I think this is the bypass hose, but where does it go?

I almost think these 2 go together, but the parts manual shows 2 different elbows here, which has me confused.

First unless you have rebuilt the engine, this could be a very bad idea. The crud that periodically dislodges in side a previously unprotected engine can clog everything up. But if you really want to do it anyway, we need your engine serial number, or at least a year to try and figure out the way it should be configured

 

[thumpar]

I agree with AllDodge. What is the history of the engine?

 

[kbeckman]

No Title

It was a 1996 Mercruiser 5.7L with a serial number of of 0F606xxx, but I ended up with a cracked head this fall and was getting water in the oil. I replaced it with a brand new 5.7L Marine non-Vortec crate motor.

Engine is already installed, but has zero hours on it. I'm wanting to install a half closed system, where antifreeze is used just in the block. The only thing I moved over from the old engine is the water pump. Everything else is new, including the intake.

 

[Volphin]

The one from the water pump goes to the intake manifold I think, need to get my glasses for the other... LOL
Maybe the other is for the temp sensor or optional cabin heater.

 

[kbeckman]

No Title

All the diagrams show it going from the water pump to the block and intake. This almost looks like the 454 setup, as there is a coolant plug on the front of the intake where this could attach. On the Injected engine, the intake has a plug there too, but a standard GM V8 like my GM 5.7L does not have that port. There is the one off to the side, that was normally a heater hose on cars, so maybe that where it goes. I know this is for the thermostat bypass, for when the engine is cold.

The one next to the bleeder is probably for a heater.


I found this diagram which shows the hose better, but that port is not there.

 

[Scott Danforth]

keep in mind, the T-stat housing is different between the two types of cooling. did you get a kit with appropriate parts and instructions, or are you trying to simply install a HX on the motor?

 

[alldodge]

As Scott mentioned your going to need a different thermostat housing. This one is for a GM 350 and includes an inboard transmission cooler. Note the cooling going to the exhaust elbows come from the heat exchanger separately.


On this one there is a Tee fitting which takes a single out put from the heat exchanger and sends it to the exhaust elbows

 

[kbeckman]

No Title

I picked up a slightly used Mercruiser Closed cooling system, as pictured in my first message. It came with the new thermostat housing, and all I'm trying to figure out is the bypass hose that comes off the top of the V8 water pump, and goes to the engine. It's green in the diagram.

I believe this can be left off the 5.7L, as there is already Thermostat bypass built into the system. Here is a coolant flow diagram:

 

[alldodge]

I picked up a slightly used Mercruiser Closed cooling system, as pictured in my first message. It came with the new thermostat housing, and all I'm trying to figure out is the bypass hose that comes off the top of the V8 water pump, and goes to the engine. It's green in the diagram.

I believe this can be left off the 5.7L, as there is already Thermostat bypass built into the system. Here is a coolant flow diagram:

Edit: maybe, let me do some more checking. There should be a port on the bottom of the thermostat housing which a fitting can be installed to go to the water pump

 

[alldodge]

Something didn't sound right about not having the hose. The hose should be there and uses a NPT to barbed fitting. This is a marine intake shows the opening on the left side besides the thermostat opening

 

[Volphin]

Is the system you are installing a full system (manifolds & block) or a half system (block only)?
Nevermind.. just saw your diagram. Half system.

 

[kbeckman]

No Title

The stock iron manifold has a port on the left side that I could use to hook up to the water pump, or I could use the one I was describing originally, that is on the thermostat housing (See pic). Both are hot water out ports, so either could be used.

I still don't think either is necessary, as the Mercruiser heat exchanger has a thermostat bypass already built into it. If you look at my color diagram, the yellow hose gives you thermostat bypass when the engine is cold.

 

[kbeckman]

As Scott mentioned your going to need a different thermostat housing. This one is for a GM 350 and includes an inboard transmission cooler. Note the cooling going to the exhaust elbows come from the heat exchanger separately.


This is a full system, and I have a half system. It's the same though, and shows the top port on the Engine mounted water pump going to the center of the intake manifold. A GM Small Block V8 does not have a port there, but Big Blocks do.

On this one there is a Tee fitting which takes a single out put from the heat exchanger and sends it to the exhaust elbows

This is a rear mounted full system, which is very different. Note that there is no hose going from the top of the water pump to the intake though.

 

[alldodge]

This is a rear mounted full system, which is very different. Note that there is no hose going from the top of the water pump to the intake though.

Your trying to install a rear mount HE and not a front mount as in your pic? Such as one below

 

[kbeckman]

No, I already installed a front mount. The big question is whether or not I'll install another bypass hose from the top of the engine water pump to the intake. I looked at the San Juan installation and they don't use the extra bypass on the 5.7L.

Look at your picture. The hose right near #11 goes from the top of the water pump to the center of the intake. This is for Big Blocks. A Small block doesn't have a port there. There is a port on the left side of the intake

 

[alldodge]

IMO even the SB needs to have a thermostat bypass. This is either done by a hose coming from the top of the pump or by using a bypass hose with the thermostat housing you posted previously. The fitting on top would not need to be used with this housing unless a hot water heater was installed. Buy using this one your exhaust manifolds and elbows will be raw water cooled.

If you use this one a bypass would be needed and the manifolds would be part of the closed cooling system

 

[kbeckman]

No Title

The one I installed has a bypass, which is why the thermostat is mounted sideways. Look at the yellow hose, it is the bypass

 

[alldodge]

Yes I know, I understand, I have seen and understand your position and have given my opinion. I can only hope that someone else will provide their input and maybe another opinion which may better suit what your wanting as an final outcome