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Old 11-15-2017, 12:42 PM   #21
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Originally Posted by Xsbank View Post
Can you show us some more photos of the installation?
Here are a couple pics of the 2" hot discharge from the tstat going around to the back of the engine to the transmission cooler in a full series loop, and the into the exhaust manifold cooler box before exiting the er to the 1 1/4" keel cooler under the hull. Too much backpressure to meet the engines maximum friction head after engine outlet of 3 psi.
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Old 11-15-2017, 04:29 PM   #22
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If I am seeing this correctly, I would run the hot water from the engine (it will only do that once the thermostat is opened) directly to the keel cooler. I would find a place to tap the jacket (same as you would for a heater connection) and run that through the transmission and hydraulic cooler. The water returning from the KC I would run directly to the engine. That is the way mine is plumbed. Your transmission has a plate on it that will tell you how hot the oil can get, that is a higher limit than what the engine can take.

If you have a loop to a water heater, remember it will also heat up the coolant if it is electrically heated. I would disconnect that loop (connect it in a loop outside the tank) for the time being.

I don't see an overflow bottle. You need a big one (at least a gallon, preferably 2) and it should be mounted above that header tank so that the system will be self-bleeding. I have a Murphy switch on mine in case I spring a leak and start losing coolant. That will be hard to do with your limited space - it might need to go in a cupboard or similar.

I think that without a heat exchanger for the engine and running the others off a loop, not the KC, you will have sufficient cooling if the engine is healthy.

By the way, that red hose looks like its time to change it too.

Good luck!
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Old 11-15-2017, 06:13 PM   #23
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Quote:
Originally Posted by Transaxial View Post
Here are a couple pics of the 2" hot discharge from the tstat going around to the back of the engine to the transmission cooler in a full series loop, and the into the exhaust manifold cooler box before exiting the er to the 1 1/4" keel cooler under the hull. Too much backpressure to meet the engines maximum friction head after engine outlet of 3 psi.
Most transmission coolers are too restrictive to be in the main 2" circuit. The pump bypass malfunction was a very good idea did you ever valve or block it for a test?
I changed over my engine, same aprox HP, from sea water to freshwater cooling many years ago on my lobsterboat. I increased the area of the heat exchanger by 25% as a precaution and has always seemed to be plenty. However I created a parallel flow path b/c the manifold did not have 2" ports nor could they be installed.
In New England many people run dry stacks but I have yet to see a watercooled one. Cooling the manifold is one thing but depending on how much and how cool the piping is it seems to me you could more than double your cooling load.
As an aside: My friend and I just built a harbor launch and used a 45HP antique gas engine with WC manifold. We used the cooler pipes that came with the engine 17' 3/4" pipe. And the propeller so basicly same load. It overheated right away at full load. We increased the length to 30' and problem solved. Maybe the engine was never run at full power b/4. 3/4" pipe is 1" OD so 30' gives maybe 8 sq feet area about 5.5 HP per sq foot.
If I read correctly, you have 13 sq' of area or nearly 10 hp per sq. foot.
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Old 11-15-2017, 11:01 PM   #24
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I think there is some terminology confusion going on here.

The cooled dry exhaust that you describe is more commonly called a wet exhaust manifold and is very common on marine engines. In fact, they are almost universal.

The heat rejection spec for your engine should include everything in the engine coolant loop as supplied by the mfg. This would typically include the main engine water jacket, but also include the wet exhaust manifold. Now I say "should", but its always possible that the spec you have is for the non-marinized engine which would normally not have a wet exhaust manifold. Perhaps there are other clues in the engine specs about whether they are talking about the marine version of the engine? For example, if they talk about the sea water pump, then the spec is surely for the full marine engine and would include coolant heat rejection from the wet manifold.

In contrast, the gear cooler would typically NOT be part of the engine heat rejection spec. However I expect it is minuscule compare to the engine, so not a concern from a heat rejection stand point.

As a reference point, a modern Deere 160HP engine rejects about 350kBTU to the coolant circuit. So something in the 250KBTU range for your engine seems reasonable.

Another point of miscommunication I think has to do with the bypass circuit. Cooling systems have an internal bypass path to allow coolant to continue to circulate while the engine is warming up. You shouldn't screw around with that in any way, and as has been pointed out, using the wrong type of thermostat can defeat the bypass causing all sorts of problems.

Separate from the bypass is the aux heating loop commonly used for heating domestic water and heating the cabin. It has nothing to do with the bypass circuit. The aux heating loop is the thing that is optional and can b valved off or plugged if desired. Manufacturers will also commonly like flow through the aux loop using fittings with fixed opening sizes, and limiting the size of allowed hose, all to prevent over cooling of the engine. I cant tell which of these you have modified, but neither may be a good idea.

BTU specs are one thing, and as you have surmised, unimpeded coolant flow is another thing entirely, and yours indeed seems suspect. A 2" engine hose size, going to 1.5" for the manifold is not great, but I see nothing you can do about that. The subsequent drop to 1.25" for the gear cooler, hose runs, and keel cooler seem very problematic.

But before making any changes, I totally agree with DMarchand and Ski about diagnosing the problem before you plan the remedy. Unless you are getting hot coolant out of the keel cooler, you should assume the cooler is fine.

Another good test would be to measure the coolant pressure somewhere between the pump outlet and the entrance to the gear cooler. You mentioned calculations in the 25 to 35 psi range which is nutty. Specs I've seen call for no more than something like 5 psi back pressure through the external loop. I think your suspicion is correct that you just aren't getting sufficient flow. But temp measurement along the path will confirm one way or another.

I suspect that if you bypassed the gear cooler and ran 1-1/2" or even 2" hose to the cooler that it would work fine, even with the step down to 1-1/4" through the cooler itself.
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Old 11-16-2017, 06:43 AM   #25
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Some more info passed to me....


"Unless you are getting hot coolant out of the keel cooler, you should assume the cooler is fine."

If the flow through the cooler is restricted you can put boiling water in one end and get ice water out the other. This is a heat transfer exercise, there is a difference between heat and temperature. If you pass a small quantity of high temperature coolant through the heat exchanger over a long period the number of BTUs required to be removed to drop the temperature may be quite small. In that case the temperature difference between inlet and outlet is essentially meaningless.

If the coolant flow through the engine is at the design rate and the temperature drop across the heat exchanger is low then it may be assumed the heat transfer area of the cooler is inadequate or is fouled externally.

"I think your suspicion is correct that you just aren't getting sufficient flow. But temp measurement along the path will confirm one way or another."

Temperature measurement alone will not confirm anything other than the temperature at the point of measurement. If the OP correctly determined the rate of coolant flow it is less than 20 percent of design rating so it should be no surprise if the limited number of BTUs entering the keel cooler will be removed and produce a misleading low temperature output while the engine overheats. If flow rate is correct then the temperature differential across the heater is a valid measure of heat exchanger capacity or efficiency. Neither flow nor temperature differential alone should be used as a measure of system efficiency.

His original post stated categorically that the manufacturer's required flow is 58 GPM but actual flow was measured at only 10GPM and stated the engine overheats rapidly when a load is applied. Why all the discussion? It is like someone saying that their light bulb suddenly went dim and when they checked the voltage it was very low but wants to know if something is wrong with the bulb.
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