Dry exhaust

I am trying to work out a cooling problem on a raw water cooled Crusader 270. Will it cause any problems (to elbows, hoses, muffler...) if I divert the raw water coming out of the heat exchanger into the bilge so just the exhaust gases are going into the exhaust system?
Thanks.

KAG said:

1.... I am trying to work out a cooling problem on a raw water cooled Crusader 270. Will it cause any problems (to elbows, hoses, muffler...)

2.... if I divert the raw water coming out of the heat exchanger into the bilge so just the exhaust gases are going into the exhaust system?
Thanks.

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1.... Short answer...... for a very quick and short 10 to 20 second start up... NO!

However, if you run for much longer, you'll risk blistering the interiors of the rubber exhaust coupling components, and it certainly won't do any good to the fiberglass mufflers.
These components are intended to be wet.


2... If you have a Heat Exchanger, your engine is not Raw Water cooled.



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1. Thank you. I will try and rig a diverter so at least some water goes through the exhaust.
2. Whoops. I have been so focused on the raw water side that I misspoke. It is "fresh water" cooled. At least it used to be, it is not cooling enough anymore.

I don't understand. Why would you want all that water to go into your bilge? Is it just for a quick test of the quantity being pumped? Will you be catching it in a bucket to measure the amount for each side?

Kag,
You want all the water going through the exhaust as it is meant to. Reason is that it keeps it cool so you don't burn your hoses off.

erich said:

I don't understand. Why would you want all that water to go into your bilge? Is it just for a quick test of the quantity being pumped? Will you be catching it in a bucket to measure the amount for each side?

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It is a test. I have an overheating problem that I have tried all the usual (and then some) things to resolve, without luck. The raw water discharge goes to a T then into the exhaust elbows, through a connection with is reduced compared with the HX discharge hose. I am wondering if that is restricting flow to the extent that if I can remove some of the reduction I will get more flow so more cooling. It is not the source of the problem since it has always been set up that way (as is the other motor) but since I can't figure out what the problem is I am hoping this will compensate for it and at least allow normal operation of the boat. (I don't intend to operate with the raw water going into the bilge as a solution, only as a test, if it seems like it helps I will rig something up that discharges it all overboard, including through the exhaust.)

Kag,

If you describe the overheating problem you are having with some details such as at idle, at cruise, after coming off cruise, etc. etc. And then tell us what you have done so far, perhaps we can offer some things to try that you haven't thought of.

Erich

Erich: It is a problem that goes back two years, and is part of the reason the boat didn't go in last year, that I am finally getting back to. There is a long thread from 2012 headed, I think "Overheating Problem" that gives all kinds of details. It is the only other post under my user name so is easy to find. Feel free to review and it would be great if you could offer any insight. At the time I got lots of suggestions, which I appreciated, but the problem remains so I am back to trying to pin it down, or at least make it work.

Looks like I may have a lot of reading ahead of me...3 pages.

I was having an issue with over heating the past couple of years and I think that I have it solved. My raw water pump was in desperate need of rebuilding. I have a Sherwood E-38, The face plate was worn, the bearings were shot. The seals were not leaking but the cam was worn down. I just got put over and so far I am down around 40 degrees on average. So if youve not looked your pump over I would suggest you do. I tried to upload photos to show you the parts but was unable to.

Kag,

I found that old thread http://www.marineengine.com/boat-forum/showthread.php?401984-Overheating-problem and quickly read through it, mainly reading your posts. I believe you swapped the HX between the OK engine and the mis-behaving engine and there was only a slight change. Correct?

I don't see that you also swapped the raw water pumps but came to the conclusion that the problem was not on the raw water side. If you did not swap those raw water pumps I think you should try that.

Did you try swapping the thermostats? Even a new thermostat can be defective.

Erich

A few years earlier one of my raw water pumps was leaking, so I replaced them both. When this problem arose I replaced the impellers. I did not swap the pumps because they are both relatively new and the flow seemed adequate (and about the same from both). In 2012 I was as confident as you can be without knowing what the problem actually is that it was not raw water flow (so couldn't be the pump). I still feel that way but, as mentioned above, think if I can increase the raw water flow it might help (treating a symptom, not the disease, I know but I am stymied as to the disease). I also did not swap thermostats as I bought a new one (which I later drilled holes in) and ran with and without one (with a minor but measurable difference, but still too hot regardless). I suppose I could do it (the swaps) to be certain. (Yes, I did swap the HXs, minimal difference)

I read some of the old thread. You have tried about everything. I know that you looked at the circulating pump, but I hope that you are absolutely sure (by checking numbers, not just by observation) that it is correct for your reverse rotation engine.

another two years of corrosion has occurred in the exhaust elbows....I'd be inclined to verify nothing else has degraded in that time, too.

If the engine temp will rise while sitting at the dock, you can always substitute the dock hose for the "raw" cooling water to see if that has any change.

CaboJohn said:

I read some of the old thread. You have tried about everything. I know that you looked at the circulating pump, but I hope that you are absolutely sure (by checking numbers, not just by observation) that it is correct for your reverse rotation engine.

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From the old thread:
"Another sunrise trip to the boat, this time to pull the water pump (engine, not raw). It is a GM pump, #3839175, which seems pretty standard. The impeller is stamped GM 6269981 MB. The shaft appears to be ss and the impeller bronze with straight fins. Which, I think, makes it a marine, bi-directional pump (right?). There is no apparent physical damage and it spins freely. Other than out of desperate need to do something, I don't think it needs to be replaced, unless I am wrong and it is the wrong pump, in which case I would need some advice as to what to replace it with."

Those are the numbers on the pump but I haven't had any luck determining if it is the proper one. I do know it is the one that has always been there, but that doesn't necessarily mean it is the correct one or that another one wouldn't work better.

I had a similar problem 2 years ago. I changed everything and did pretty much what you did as well. It turned out to be mussels growing inside the sea strainer pickup. After spending over $2000, it was $20.00 of barnicle killer that solved the problem. I would not have believed it if I did see with my own eyes!! I blocked off the intake, put a clear hose on the output side of the strainer and filled the hose. Within minutes desolving pieces of shells floated up the hose. The engine temp went from over 200 degrees to 160 and hasn't moved since! P.S., even stranger, it only happen to one side but I did both anyway!

CaboJohn said:

I read some of the old thread. You have tried about everything. I know that you looked at the circulating pump, but I hope that you are absolutely sure (by checking numbers, not just by observation) that it is correct for your reverse rotation engine.

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I had the same thought until I read the post below.

KAG said:

From the old thread:
"Another sunrise trip to the boat, thistime to pull the water pump (engine, not raw). It is a GM pump, #3839175, which seems pretty standard. The impeller is stamped GM 6269981 MB. The shaft appears to be ss and the impeller bronze with straight fins. Which, I think, makes it a marine, bi-directional pump (right?). There is no apparent physical damage and it spins freely. Other than out of desperate need to do something, I don't think it needs to be replaced, unless I am wrong and it is the wrong pump, in which case I would need some advice as to what to replace it with."

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If the bronze impeller fins/blades are rather straight, I belive that this would satisfy the bi-directional criteria.
However, I've seen a small difference in the castings for the bi-directional Circulating Pumps.

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Basically you'll have two sides to your cooling system...... the seawater side, and the E/G (ethylene glycol) side.

If the Heat Exchanger E/G is removing engine heat effectively (via the seawater), the Heat Exchanger's temperature should be cooler than engine temperature.
If the Heat Exchanger E/G is not removing enough engine heat, the E/H's temp may be much closer to engine temp... in which case the seawater flow might be inadequate.... or the E/G side of the tube bundle is not up to par (perhaps rust scale debris build up).


Typically... a good working cooling system will provide more seawater cooling than actual engine demands.
What seawater the engine cooling does not demand, simply passes along to the exhaust system, and out with the exhaust gasses.



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RicardoMarine said:

What seawater the engine cooling does not demand, simply passes along to the exhaust system, and out with the exhaust gasses.

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Actually, all of the seawater passes thru the heat exchanger and then into the exhaust...the cooling load (that the engine creates) will drive how much of a temperature rise the seawater undergoes for any given system design...

Rather than divert the raw water I decided to take another stab at actually finding out what is wrong.
I installed some clear hose in the E/G line (the antifreeze return from the exhaust manifolds to the heat exchanger). Initial observations suggested flow on one side was reduced, there was air in that side and there was no flow at idle on either side (I thought of not reporting that at all since it didn't repeat and I don't want to go off on tangents but it might suggest something to someone). That was not verified by subsequent observations, except as to air. There consistently appears to be bubbles in both sides (fairly large, but they get smaller and more mixed in as it runs). Bubbles can affect heat transfer, so could be the problem.
Before I posted anything (asking what could cause the bubbles, because I have no idea, I wouldn't expect any air except in the collection area, where these hoses empty and then the fluid flows by gravity into the actual HX) I thought I would move the clear hoses to the other engine and compare. I moved the hoses, but can't get that engine to start, so no comparison to report. Once I get it running I will report back but feel free to comment in the meantime.

makomark said:

RicardoMarine said:

What seawater the engine cooling does not demand, simply passes along to the exhaust system, and out with the exhaust gasses.

Click to expand...

Actually, all of the seawater passes thru the heat exchanger and then into the exhaust...the cooling load (that the engine creates) will drive how much of a temperature rise the seawater undergoes for any given system design...

Click to expand...

Mark.... you are correct!!
But let me clarify my comment.

The seawater pump supply (in terms of BTU removal) is typically greater than what engine cooling demands are... meaning that the seawater quantatee (I.E., flow) has more heat removing capability than what the entire system demands.... whether it be a RWC engine, or an engine fitted with Closed Cooling.

If the seawater's BTU removal capacity did not have this ability.... we'd all be much closer to an Over-Heat scenario on a daily basis.


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