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I think it does block the return to the tee. Water gets diverted out the exhaust then the pump pulls in new water from outside. Out does work.
I have the fresh water kit, but the exchanger developed a crack and won't hold water. I removed the exchanger and second pump to convert back to raw water cooling. I'm on fresh water so I'm not real concerned with internal corrosion. This is only my second year with this engine so I don't know it's history or how the crack happened.
 

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I am not familiar with engines that divert raw water from the exhaust with a thermostat. Sounds great if it works well but if not.... But I just want to add one thought to the discussion, something I have a lot of experience with. Pinholes can develop in exhaust elbows as they are probably the most corrosion prone area on a boat - hot gases, sea water....

I would just want to be sure that a very tiny pinhole had not developed and letting out just a bare amount of water which is then evaporating as steam. From the discussion that sounds like that is not the scenario here but I'll throw it out anyway. Elbows fail, much more often than people realize, and they fail from the inside out. A tiny hole or crack is the first sign and then a catastrophic failure is next. You can imagine how serious that could be as water and exhaust would be entering the boat. It often goes unnoticed underneath the high temp exhaust riser wrap.
 

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Start with the easiest, that being the strainer for water flow, then move on down the line. I would do the impeller second. If you have not replaced it in the last year or so it would be good to do that at this time.
 

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Discussion Starter #24
Someone please educate me. Why does the raw water after passing through the engine go out trough the exhaust?

I did go to my boat yesterday and took the thermostat out. Time will tell if this will eliminate the steam problem.
 

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the raw water cools the exhaust hose. without the water you would have dry exhaust like a car running through the boat with insulation on it keep from burning things. you have the water brought into cool the engine and it has to go out somewhere. the exhaust is the best way to get it out of the engine.
 

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Someone please educate me. Why does the raw water after passing through the engine go out trough the exhaust?

I did go to my boat yesterday and took the thermostat out. Time will tell if this will eliminate the steam problem.
Be VERY careful!! With the standard raw water system on the 5411, with the thermostat out, it goes into full recirculation mode. That means the engine will overheat after being run for a few minutes. That was the reason the PO put a manual valve in the recirc line. It restricted the recirculating water and forced some out the exhaust.

Again, if your temperature is fine i.e about 140 to 150F, just ignore the water vapor (steam). You are creating a problem in your mind where there isn't one. And running the engine too cold will not do it any good.
 

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Why steam? Well even tho your engine is at 140 deg, the exhaust is well over 1200 deg. With the use of a riser the part of the exhaust pipe with no water in it will be well over 180 deg needed to make steam. When you inject 140 deg onto a 800+ deg exhaust pipe, you are going to get some steam.

When I changed my dry exhaust system with a modern wet exhaust, I was amazed the the best flexible exhaust pipe I could get was rated for 250 deg. and the use of a Fiberglas muffler. That scares the hell out of me. It would take no time at all to have a fire if there is no water being pumped. First thing I check when i start the engine is the water coming out.

My original exhaust was a dry system. No water in the exhaust pipe. It had a double walled brass pipe with the exhaust in the middle with water jacket around it. When it failed after 30 years, it could not be fixed or even removed in one piece. The boat was built around it. It was hard pipe from the exhaust manifold to the transom. and the engine was hard mounted.

I would not use a thermostat on your setup. No water in the exhaust for a worm up time could be catastrophic. My engine has no problem coming up to temperature with raw water.

Side note... my 1968 flat head Graymarine Seascout 91 25 hp gas engine with raw sea water cooling is in tip top shape. I removed it 13 years ago when the exhaust pipe failed and got a hole in the water jacket to the inner exhaust pipe. Because my engine is at or below the water line, I got back siphoning into the engine. Went I took the engine apart, it needed nothing but a good clean out. I do have two zinc pencils in the head I replace every year. Also, with the change from dry to wet exhaust, it was critical to add the riser and vacuum breaker just before the water hits the exhaust. I also added a high temp alarm.
 

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I would not use a thermostat on your setup. No water in the exhaust for a worm up time could be catastrophic. My engine has no problem coming up to temperature with raw water.
No! As I noted in the post above, removing the thermostat in the 5411 results in the system going into recirculation mode and the engine will overheat. As was noted in post #16, the 5411 thermostat has bypass holes in it which provides a minimum flow into the exhaust. The flow into the exhaust is never zero but does increase or decrease with engine load.
 

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I did not think I had to mention the need for a valve to cut off the recalculation and and have all the water going straight out the exhaust. Sorry for being vague.
 

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Discussion Starter #30
My system does have a valve. When closed the engine temp. only gets to 110 degrees. Open it over heats. Put thermostat in and open valve, temp. rises to 150 degrees and you have a lot of steam.

For the past 7 yrs she has run with the valve closed. Engine is in good condition. But I know a diesel needs to run 140 or hotter. That is my goal. I am trying to eliminate some of the steam.

Thanks for your input. I have learned a lot about my problem. I will keep experimenting till I find the solution.
 
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