Cooling question

[MJPesky]

I was in touch with Mercruiser and they ran my serial numbers for my 7.4' s. They told me I have raw water cooling. Here's a photo of my manifold and elbow. I will be replacing both or maybe just a cleanup and bolts and gaskets. These manifolds are actually fresh water cooled correct? They have two lines to them with a separate raw water line to the elbow. Thanks for any info. I'm thinking maybe this was done aftermarket? But the main question is that these manifolds are antifreeze cooled with the block correct?

 

[scoflaw]

Hard to say what you have going on there, pic is not the best, should have backed up a bit and your not offering up the engine number. It should be obvious when you take it apart. Go with a dry-joint system when you replace it

 

[Happy Hour IV]

Sure is lots of misinformation out there. I will not add to it, I do NOT know what a rolled exhaust cooling system is. I do know that the 7.4 manifolds are not available with the configuration for
dry stack. The 496 manifolds, contrary to popular belief, do fit the 454. It does require
a modification as the riser has a different angle (if memory serves it is 7.5 degrees off). The 496 manifolds are setup for raw water cooling only (not coolant). One step further the 496 manifolds are no longer made in aluminum because of the failure rate in saltwater. However with some modifications,
the ebay available aluminum manifolds can be plumbed in with coolant flow rather than raw water.
The result is a significant weight savings, longevity on the manifolds, no leakage issues at the riser gaskets, and a little better exhaust flow thru the manifolds. I would be very interested in understanding what a rolled cooling is. If verbal could you have misunderstood raw water cooling?

 

[Espos4]

If exhaust manifolds are cooled by antifreeze, you should see some sort of block off plate/gasket between the manifold and riser.

I believe risers are always raw water cooled, so any gasket that allows water to pass between the the riser and manifold would indicate that the manifolds are raw water cooled.

 

[scoflaw]

If you attempt to get the manifolds in the closed loop AF side your going to need a big-ass heat exchanger.

 

[Stee6043]

I'd put my money on your Merc guy having a lip full of chew when he explained to you that you have raw water cooled 7.4's. As a result what you, and any other sane person on the other end of that Skaol-fueled conversation, would have heard was "rolled water cooled".

Just guessing here

 

[MJPesky]

Another photo.

 

[Stee6043]

Another photo.

That's a freshwater cooled motor. Not raw water...

 

[scoflaw]

Closed cooled is the correct term. Plumbed different from what I've seen. Does it work as intended?

 

[ttmott]

Is not the closed loop cooling including the exhaust manifolds referred as the Mercury Horizon engine?

 

[Stee6043]

Closed cooled is the correct term. Plumbed different from what I've seen. Does it work as intended?

Not if it's sending raw water into the exhaust...the plumbing for which I believe the OP showed in his first post above.

So...I believe freshwater cooled is the correct term

 

[scoflaw]

Every system sends raw water to the exhaust. Full CC system would include the manifold with the AF, raw water to the elbow for discharge. Half system would be AF in the block only, raw water to manifolds exiting the elbows.

 

[mrsrobinson]

Every system sends raw water to the exhaust. Full CC system would include the manifold with the AF, raw water to the elbow for discharge. Half system would be AF in the block only, raw water to manifolds exiting the elbows.

This is what I upgraded the 7.4s to in my 95 330DA; engine and manifolds were "antifreeze fresh water" cooled, full closed system

OP, I see lots of rust/corrosion in your riser/manifold connection. I'd take them apart ASAP, at a minimum replace the gaskets.

 

[hughespat57]

Regardless of OEM names it's either
Full closed system (with manifolds)
Half closed system (block only)

Risers are always salt (raw) water cooled
The manifolds have a top and bottom hose to the exchanger
The risers have a shared split hose from the end of the exchanger, (raw)
Raw water always flows from one end to the other of a tube heat exchanger
Antifreeze/coolant flows out the bottom to the circulating pump and back via the thermostat hosing.
Here plumbing can vary by OEM but some method will allow coolant to always flow thru the manifolds even if the thermostat is closed for the engine.

 

[MJPesky]

OK... SOOOO Here is where I am at and correct me if I am wrong. The serial #'s list my engines with mercruiser as raw water cooled 7.4's , so this system must have been installed aftermarket. It has a mercury 814864 heat exchanger with lines to the manifolds which I believe makes it a "closed loop" cooling system with AF in the manifolds and a block off plate between the manifolds and elbows (I have no spacers). Obviously there is some corrosion visible. My plan of attack is to remove and inspect them internally. If they are in good shape, clean the oxidation off, paint and re-install with new manifold and elbow gaskets and bolts. I was told that the elbows are "stainless lined", so they should be in good shape internally also. Sound like a plan??? Thanks for all the help guys!!!!!!

 

[mrsrobinson]

OK... SOOOO Here is where I am at and correct me if I am wrong. The serial #'s list my engines with mercruiser as raw water cooled 7.4's , so this system must have been installed aftermarket. It has a mercury 814864 heat exchanger with lines to the manifolds which I believe makes it a "closed loop" cooling system with AF in the manifolds and a block off plate between the manifolds and elbows (I have no spacers). Obviously there is some corrosion visible. My plan of attack is to remove and inspect them internally. If they are in good shape, clean the oxidation off, paint and re-install with new manifold and elbow gaskets and bolts. I was told that the elbows are "stainless lined", so they should be in good shape internally also. Sound like a plan??? Thanks for all the help guys!!!!!!

With the exception of "stainless lined", sounds like the right plan.

 

[Brite Idea]

Looking at the picture I'd say yes disassemble and inspect. Here's my concern, how old are the manifolds and risers? The boat is a 1996 but does that mean all of the exhaust is that old? If so just remove all the exhaust components and replace with new everything. My reasoning is that even closed cooling manifolds have a life expectancy and if yours are original they're DONE!

 

[MJPesky]

Looking at the picture I'd say yes disassemble and inspect. Here's my concern, how old are the manifolds and risers? The boat is a 1996 but does that mean all of the exhaust is that old? If so just remove all the exhaust components and replace with new everything. My reasoning is that even closed cooling manifolds have a life expectancy and if yours are original they're DONE!

I purchased the boat from a friend. He said he did manifolds and elbows 5 years ago. I think I'll know a lot more after I pull it all apart. The other thing I have to look into is why both engines only ran at a max of about 140° and even cooler when the water temps went down at the end of the season.