2007 8.1 Gi converted to rear-mount closed cooling

apw30534

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Ordered this kit from Hardin Marine last Fall and had to wait for my garage to be finished before tackling the project. Finally took care of it this past weekend.
The kit was relatively simple to install, but due to my engine/hull combo... needed some extra fab work to make it fit/function properly.
The biggest issue was the tank mounting location and brackets included in the kit. In most hulls this probably works fine, but my engine sits pretty low and the tank would have been resting right on top of my power steering cylinder. I had to modify the brackets and raise the tank a few inches for clearance.
The rear mounted tank also created an issue with my hatch motor/strut assy... and required that I relocate that too.
The fuse box was another issue and I needed to make a bracket to raise it and move rearward a bit to make way for the coolant hose running alongside the intake.
Also had to move the ground cables at the rear of the engine to make way for a hose to pass through the same area.

None of these issues were a really big deal... but for the cost of this kit, should have included some alternative brackets or accessories to accommodate different hull/engine packages.
The instructions were also terrible and the pictures not much help.
Having an understanding of where the water and antifreeze need to separate and flow is the biggest help for an installation like this.

Haven't had it in the water yet but it runs up to temp in the driveway while on the hose.

Video of it running:
 

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tpenfield

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I installed the SJE (now Orca) closed cooling kits on my twin 454's about 10 years ago. I agree on the instructions being vague . . . you sort of had to figure things out on your own. So, I guess that short-coming has not changed. It makes these kits a little higher on the 'DIY difficulty scale' than they could be.

Is this full closed cooling? (hard to tell from the pictures)

I never liked the thermostat configuration/design and I ended up going with a modified thermostat to provide more bypass for the engine warm-up cycle. Not sure if you have noticed any similar problems.

Looks like the engine hatch lift was right in your way. Of course, a front mounted system would have the air intake in the way. :unsure:

Nice job!
 

apw30534

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I installed the SJE (now Orca) closed cooling kits on my twin 454's about 10 years ago. I agree on the instructions being vague . . . you sort of had to figure things out on your own. So, I guess that short-coming has not changed. It makes these kits a little higher on the 'DIY difficulty scale' than they could be.

Is this full closed cooling? (hard to tell from the pictures)

I never liked the thermostat configuration/design and I ended up going with a modified thermostat to provide more bypass for the engine warm-up cycle. Not sure if you have noticed any similar problems.

Looks like the engine hatch lift was right in your way. Of course, a front mounted system would have the air intake in the way. :unsure:

Nice job!
Yeah the crappy instructions were probably my biggest complaint. Nothing I couldn't get past... but would certainly cause problems for someone not as comfortable under the hatch.
This was a half kit and the only thing available. I would love to somehow get antifreeze into the exhaust manifolds too... but will need to figure that out after running it as is for awhile.
I've only run it on the hose so far... haven't had it in the lake yet but will likely get to that this weekend.

I have noticed a significant amount more water comes out of the port side exhaust than the starboard side... so hopefully that is just a driveway/hose issue vs an actual water/system flow issue.
 

Lou C

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Nov 10, 2002
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I have VP style manifolds on my OMC 4.3 and asked about this (full closed cooling) on this forum and Scott explained that you can't have VP style manifolds on a full system because you have to have 2 fittings at different heights on the manifold to allow coolant to flow in on the bottom of the manifold and out of the manifold on the top. This prevents air locks/hot spots that would result if you used the VP fittings which are at the same level front and rear. Mercruiser manifolds are designed to allow this, with a bottom inlet fitting and a top exit fitting near where the exhaust elbow bolts to the manifold.
So the only way I could have full closed cooling (which I'd love to have) is to convert to Mercruiser manifolds (not sure if it would work, due to height and angle of the exhaust elbow exit). That's assuming my Cobra impeller can deliver enough raw water flow to keep the temps in line.

PS that install looks great! Very neat, and organized.
 

apw30534

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Jan 14, 2022
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I have VP style manifolds on my OMC 4.3 and asked about this (full closed cooling) on this forum and Scott explained that you can't have VP style manifolds on a full system because you have to have 2 fittings at different heights on the manifold to allow coolant to flow in on the bottom of the manifold and out of the manifold on the top. This prevents air locks/hot spots that would result if you used the VP fittings which are at the same level front and rear. Mercruiser manifolds are designed to allow this, with a bottom inlet fitting and a top exit fitting near where the exhaust elbow bolts to the manifold.
So the only way I could have full closed cooling (which I'd love to have) is to convert to Mercruiser manifolds (not sure if it would work, due to height and angle of the exhaust elbow exit). That's assuming my Cobra impeller can deliver enough raw water flow to keep the temps in line.

PS that install looks great! Very neat, and organized.

Thanks!

And yeah... I dont think there is an easy way to do it with the existing manifolds. In addition... I have 6" riser blocks under the risers also... so that's a whole 'nuther can of worms.

In good time, I will likely upgrade to a newer Mercruiser manifold/riser set or a set of Stainless Marine aluminum manifolds/stainless risers.
 

Lou C

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now....if you have riser blocks....I wonder if those could be tapped for your top coolant exit? So your regular gasket goes between the manifold and riser block and the block off plate between the riser block and the elbow?
 

apw30534

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now....if you have riser blocks....I wonder if those could be tapped for your top coolant exit? So your regular gasket goes between the manifold and riser block and the block off plate between the riser block and the elbow?

lol... yeah the thought had entered my mind after typing the last reply.

I think I will sit tight until a better flowing set of manifolds go on the boat. I don't want to put a bunch of work into these, only to toss them on the scrap pile eventually.
 

Lou C

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My vote would be to see if you can adapt Merc dry joint manifolds, they have the best design to keep out water, and can be used with full closed cooling.
 

tpenfield

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Probably the biggest difference between the half and full systems is the size of the heat exchanger. Not sure how much bigger they are, but the ones on my 454's were the full width of the engine IIRC.
 

apw30534

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My vote would be to see if you can adapt Merc dry joint manifolds, they have the best design to keep out water, and can be used with full closed cooling.
I've been eyeballing them... just havent found the right setup yet.
The biggest issue is that I need the extra 6" riser blocks between the manifold and SS risers... which is not a common thing and they are pretty spendy.
It is nice that Merc has some aluminum manifolds floating around out there... so thats what Im looking at grabbing eventually.
 

apw30534

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Probably the biggest difference between the half and full systems is the size of the heat exchanger. Not sure how much bigger they are, but the ones on my 454's were the full width of the engine IIRC.
Yeah that is another concern. I dont know if my tank will handle the added heat load.
 

apw30534

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Just a quick update....
I've had the boat out several times and the engine temp stays rock-steady @ 160 degrees. I couldn't be happier with this kit and I'm sure the engine will live longer with antifreeze inside it.
Also just saw my best top speed last Friday.
 

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apw30534

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Great 160* is perfect. 56 mph is moving right along!
Yeah I'm super pleased with the speed. My previous Chaparral was all done @42mph.
This current 256 might even hang with a few (very few) jet-ski's. lol
 
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