15 bolts later

[jimbunyard]

Does your other engine have the same bundle? Just out of curiosity?

If I rememver correctly, the large hole in the VP original 'shrouded' bundle aligns with the hole in the H/E housing where F/W is introduced into the H/E assembly. Hypothetically, this would concentrate the hottest water mostly directly (the junction between the hsg and the bundle isn't very precise) into the bundle, where it would benefit most from the cooling effects of the raw water passage through the bundle.

If the fresh water is just flooded into the H/E housing the cooling effect is much dissipated and likely uneven.

If you find that the other engine has the original-style bundle, you may have found the culprit.

If you have a water heater installed on the malfunctioning engine, I'd still investigate the chances of air somewhere in the system.

Call me lazy, but tracing and maybe rerouting some hoses seems easier that changing an exhaust elbow --- though of course I don't know the layout of your boat...

...Which made me think of another option. If you do have a water heater, try jumping it out of the system by running a short piece of hose between the inlet and outlet connection on the engine. If she runs cool (er) you've isolated the problem.

[team karst]

I can "finger" tubes on both engines from the filler. The bundle is well up from the coolant ports. But, i'm not familiar with the internals of the HE, unclear of any internal routing, if any. There is a bottom hose attachment and one that's about 1/2 way up at the end of the HE.
On gas motors, its quite typical to run three pass HE, where the RW is routed back and forth in the hot water. Here, we obviously have a simple, single pass affair.
For me to shoot temperatures lower in the HE than the exit of the block/heads is interesting. Because the HE has the added heat from 3 cylinders of exhaust. Leading to my theory of low coolant flow; and adds credibility to air locks too. Pump looked and turned ok, so its back together and tomorrow will be a leak test. I might add Water Wetter, to increase water conduction. But, that clearly is a bandaid.

Yeah, engine access is great on all 4 sides. But the front is accessed from above. But, its "outside" in full sun, with no wind these days. The a/c space starts 5 feet forward.

[skipperpete]

Why not do the “ volume/time “ check.......stop watch and a bucket are all you need. Strap up tight at the dock, run the problem engine at about 1200rpm then put the bucket under the exhaust and time it till it fills to, say, half full then repeat the test on the other engine and compare the results. The test will tell you at least if you have a raw water circuit flow problem. It’s messy and often difficult to keep the bucket in place if the exhaust outlets are low.

[team karst]

OK, I banged out the tube bundle. No shroud at all. Trying to understand the HE design for water path(s). The middle (fore/aft dimension) of the tube bundle uses a blocked section in the HE from front to rear. Appears the front does the engine cooling and the rear does the exhaust cooling. There is no tube to blow hot engine coolant against the tubes.
But, obviously, the coolant must somehow make a transition to run both past both sections of the tubes. At this point, I quit trying to act like a water molecule and trust the design is OK. I took my brass bore brush and did all the tubes internally. They are in good shape. No impellor bits, no sig. corrosion. Not likely at all to be original.

[jimbunyard]

Originally Posted by team karst

OK, I banged out the tube bundle. No shroud at all. Trying to understand the HE design for water path(s). The middle (fore/aft dimension) of the tube bundle uses a blocked section in the HE from front to rear. Appears the front does the engine cooling and the rear does the exhaust cooling. There is no tube to blow hot engine coolant against the tubes.
But, obviously, the coolant must somehow make a transition to run both past both sections of the tubes. At this point, I quit trying to act like a water molecule and trust the design is OK. I took my brass bore brush and did all the tubes internally. They are in good shape. No impellor bits, no sig. corrosion. Not likely at all to be original.

So, you've made me got back in (sketchy) memory and to pictures, and have come up with this, though I dont think it will help resolve anything but your curiosity. See how this fits.

The hot fresh water is pumped out of the engine and leaves through the outlet that faces down. It is pumped up through the bottom of the HE hsg towards the rear, and moves forward through the housing to be cooled and exit through the horizontal hole at the front of the HE. The reason for the 'shroud' and the mid-exchanger housing partition is that, contrary to my memory, there is a large hole at each end of the original shrouded bundle, which directs a certain amount of water through the bundle, aft to fore, with the remaining F/W 'residing' in the tank as a kind of heat sink.

Of course, it could go the other way, but it seems counterintuitive indeed that you'd want cooling water to interact with the second hottest part of the engine just before being called on to perform its' primary cooling function...

[team karst]

Hmmm, something amiss. I ran the engine at 1500 spinning the prop. It reached about normal temps with the oil filter allowing maybe 1 or 2 seconds of touch.

The hot engine water appears at the short 90 deg rubber hose coming out the right side of the coolant pump, the side with the thermostat. It enters the forward vertical side of the HE. Pretty darn hot to the touch.
Down low, the coolant leaves the bottom wall of the HE thru a much longer hose to the water inlet of the coolant pump. After a significant drop in temp. Can hold this hose indefinitely.
I did connect the water heater hoses. The outbound hose was hot and the inbound cool.
Next step is take her out and do more controlled IR tests on both motors. Especially coolant in and out of HE. I’ll do 2000, 2500, and then WOT.
Oh, my canal is 90 deg water temp.

The exhaust mixer/elbow looks new inside and out.
My working theory is that low RW flow will cause high coolant temps exiting the HE.

[jimbunyard]

Have you checked the impeller on the fresh water pump?

[team karst]

I did inspect it. Looks to be stubby little steel vanes. And they r all there

This is in the area of the little 6mm passageway thru a wall. I dug it clear with a copper wire hoping it was not an intentional plug.

[team karst]

A bit of a breakthru; THis engine has a very convenient 2' long 3/4"/19mm hose from RW pump to the HE. I replaced the rubber hose with a clear, non-reinforced PVC hose. It was immediately obvious I did indeed have a suction air leak. Traced it ultimately to the RW strainer, a Vetus style plastic thing. I subbed the strainer with a simple coupler.
So, then I pressure tested the strainer with about 4 psi of air, and, NO LEAK. Then, I notice the in and out arrows are molded into the actual seal area of the plastic nipples. I sanded those down, and now, no sucked air.

Haven't yet done WOT load test, but the output stream looks more healthy.

This boat has Italian sourced RW hoses consisting of clear PVC with a sandwiched steel helical wire. Seems to not have been the issue, but it got replaced with some Shields rubber water hose.

[hpeer]

Team Karst,

Good find.

Mfg. induced failure! Neat trick.