The water flowed out here -- FOR SURE -- as expected.

Same for the starboard; FOR SURE -- as expected.

Click above for larger image.

Click above for larger image.

Now -- the un-welcomed surprise: Thinking I would find the "loop" of water flow from the front of the intake manifold (thermostat location on a car engine) to the aft end of the exhaust manifold, thru a chamber in the manifold, and forward to the thermostat housing -- I put the garden hose in the front of the long hose feeding the aft end of the exhaust manifold. The water exited the boat via the exhaust pipes -- on both sides of the boat. See next four photos:

Click above for larger image.

Click above for larger image.

Click above for larger image.

Now what? Do both exhaust manifolds have interior cracks? The PO probably had caused the engine block to crack. So maybe he had not drained the exhaust manifolds, causing cracks here too. I'd never disassembled them. Now we'd have to take them apart to find the problem. It made sense -- if the water being fed to lower portion of the manifolds continued right out the back of the boat, very little water would reach the thermostat -- only the cold water from the lake (RWP) would get there, no "warmed" water at all. New manifolds are not only expensive, they're very heavy and expensive to ship and would require some new plumbing. See?

As expected, it was bit of a pain getting the fore and aft caps off the exhaust manifolds. With a breaker bar and stubby wrenches, we got them open and looked inside. No cracks!? Maybe.

We found:
Front end cap of port exhaust manifold, same as the starboard one in background:

Click above for larger image.

That (rust thru?) opening in the center portion would let exhaust gases escape into the "lower" water passage — the passage that should carry the "closed loop" of water AFTER the engine and INTO the thermostat chamber. (WRONG — the garden hose test showed the "closed loop" was NOT a closed loop, and should be, and will be soon.) We fixed this by "gluing" a patch of steel-centered gasket material over the hole, than making a gasket with only three openings — the three "slots." (Our glue is a secret formula.) We then bolted this "cap" on the front of the port manifold. Fixed! And if you won't tell, I won't.

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Click above for larger image.

The "other" front cap, with its gasket removed, and a new gasket on left. This stuff is hard to cut -- steel center -- by Fel Pro via NAPA.

Hint -- on the aft caps we found gaskets like the one at center of 2nd photo. The aft gasket should have the large center opening, but NOT the two side slots. (Some similar designs have a "pin hole" for the side slots -- to let water leak out after engine shut-down. I'll depend on drain petcocks draining all the water in the "closed loop," and the water in the upper, "straight through" circuit will drain as it does after every shut-down.

We found some broken chunks of cast iron wedged in the passage where the cooling water enters the exhaust in the aft casting. Now fixed. We are sure neither of these situations were causing the low engine temps. Stay Tuned as we reveal the secrets.

On Apr 16, 2016, at 9:41 AM, keno439@gmail.com wrote:
Hi Grant
In the "top lifted off" picture I really can't see what holds your thermostat flange seated. It looks like the whole thermostat could float up and down.

How about a picture of the bottom of the middle piece with no gasket?

Ken,
Three photos.
Bottom and middle pieces.
The thermostat can't "move up." It's sitting on a ledge -- a shoulder -- in the bottom of the middle piece. It would be better if my hand-made gasket was more centered, but the stat can't move up (nor down).

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Click above images for larger images.

Ken, BTW - The seat that came with the new pressure relief valve is a little too large. Its OD wont let it fit in the middle piece. No big deal. I'm sure the old one is working just fine.

I now have a much better understanding of how the system is supposed to function. In a week or so, I may make an animation describing it.

4/16/16 -- It occurred to me last night that the manifold is probably not cracked. That's because the manifold was assembled with the wrong gasket configurations. (We are correcting that, and will post photos soon.)

The aft manifold fitting mates with the large part of the manifold. The gasket between the two should be open only 1) for the exhaust gases to escape and 2) for the "upper" water to move from the manifold, mix with the gases and escape via the thru-hull. (THIS STATEMENT NOT TRUE -- READ ON)

The PO (or somebody) installed a gasket (on the starboard manifold) and silicone sealer (on the port one) -- shaped so that ALL the water introduced into the front part of the manifold went through the manifold, then right out the back. i.e., NO "heated" water was being retained for the system. The ONLY water reaching the manifold was 1) cold lake water and 2) water that had been warmed by the engine block, heads and intake manifold. But all that warmed water left the boat, rather than being recirculated via the thermostat circuit. (It seemed the thermostat would NEVER open.)

When we closed shop 4/15/16, I was still worried about possible crack(s) in the manifold(s). But as I got to thinking more about it, I realized there was never any water remaining in the manifolds after shut-down. It all drained out, because none of it was retained in the cooling system -- except for the engine, which had the cracked block.

I don't have photos of the new aft gaskets -- yet. That's because before I figured out how the water SHOULD run, we made new gaskets shaped like old ones -- and the old ones were probably wrong.