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Old 10-24-2015, 11:06 PM   #1
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Lehman 135 Heat Exchanger Question

Another newbie question here. I changed the coolant on my engine a few days ago and will change the raw water impeller tomorrow. What will happen if I remove the heat exchanger end caps to take a peak inside. Will I lose the coolant or does that only give me access to the raw water side?

Thanks, Mike



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Old 10-24-2015, 11:57 PM   #2
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Mike,

Fear not- the raw water enters the cooler at one end, passes through the tubes then exits at the other end to move on to cool the transmission oil via its own heat exchanger then ultimately into the exhaust to cool that too. If you will excuse the pum, the poor sea water must be exhausted by the time it is spat unceremoniousyl out the exhaust . The exchanger is divided into three separate compartments; the ends, where the raw water enters (in one end), and exits out the other. and the larger centre section where the coolant circulates around the outside of the tubes.
The two end chambers are connected by the tubes through which the raw water passes . The coolant circulates through the centre section and gives up some of its heat to the cooler raw water that is passing through the tubes. The raw water and coolant are totally isolated so taking off the caps at each end will just allow a little raw water to escape. Not too much. Don`t forget to close the sea cock although the heat exchanger is probably above the water line.

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Old 10-25-2015, 12:43 AM   #3
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Quote:
Originally Posted by Brisyboy View Post
Mike,

Fear not- the raw water enters the cooler at one end, passes through the tubes then exits at the other end to move on to cool the transmission oil via its own heat exchanger then ultimately into the exhaust to cool that too. If you will excuse the pum, the poor sea water must be exhausted by the time it is spat unceremoniousyl out the exhaust . The exchanger is divided into three separate compartments; the ends, where the raw water enters (in one end), and exits out the other. and the larger centre section where the coolant circulates around the outside of the tubes.
The two end chambers are connected by the tubes through which the raw water passes . The coolant circulates through the centre section and gives up some of its heat to the cooler raw water that is passing through the tubes. The raw water and coolant are totally isolated so taking off the caps at each end will just allow a little raw water to escape. Not too much. Don`t forget to close the sea cock although the heat exchanger is probably above the water line.

cheers
Ah, I would suggest a rethink on that. I just changed the zincs in my exchangers, and the zinks go into the raw water part, and it is not contained in 'tubes' or you'd never get the zincs into them. The raw water is in the larger volume around the tubes, and the engine coolant and the oils, (in the case of the engine oil and tranny oil exchangers), are in the 'tubes' I think you would find. Admittedly, my engine is the 120hp, but here is the item below...

https://www.google.com.au/search?q=F...vWqla_ZJDWw%3D
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Old 10-25-2015, 01:40 AM   #4
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Ah, I would suggest a rethink on that. I just changed the zincs in my exchangers, and the zinks go into the raw water part, and it is not contained in 'tubes' or you'd never get the zincs into them. The raw water is in the larger volume around the tubes, and the engine coolant and the oils, (in the case of the engine oil and tranny oil exchangers), are in the 'tubes' I think you would find. Admittedly, my engine is the 120hp, but here is the item below...

https://www.google.com.au/search?q=F...vWqla_ZJDWw%3D
No, the raw water flows through the tubes and the coolant flows around the tubes. The zincs fit in a space between the ends of the tubes and the end cap.

And that picture is not of a heat exchanger for a Lehman 120 or 135. Or at least not one I've ever seen on a Lehman.
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Old 10-25-2015, 02:36 AM   #5
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No, the raw water flows through the tubes and the coolant flows around the tubes. The zincs fit in a space between the ends of the tubes and the end cap.

And that picture is not of a heat exchanger for a Lehman 120 or 135. Or at least not one I've ever seen on a Lehman.
So, are the zincs into the raw water or the coolant. To me, the latter makes no sense, as the coolant has anti-corrosive in it anyway. If into the raw water chambers, which makes more sense, being salt water to boot, the placement in relation to the tubes is hard to picture.
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Old 10-25-2015, 06:38 AM   #6
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Brisyboys mental picture sounded correct to me fo the several heat exchanges I have cleaned.


The raw water goes through the tiny tubes and so do the zinc/impeller parts and that's why they require periodic cleaning and rodding.
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Old 10-25-2015, 06:45 AM   #7
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Ah, I would suggest a rethink on that. I just changed the zincs in my exchangers, and the zinks go into the raw water part, and it is not contained in 'tubes' or you'd never get the zincs into them. The raw water is in the larger volume around the tubes, and the engine coolant and the oils, (in the case of the engine oil and tranny oil exchangers), are in the 'tubes' I think you would find. Admittedly, my engine is the 120hp, but here is the item below...

https://www.google.com.au/search?q=F...vWqla_ZJDWw%3D
Sorry Peter, you are less than correct - or to put it another way, you are wrong. I can say this with confidence because I have just had the ends off the main cooler of one of my engines (SP135). When I unbolted the centre bolt of each end cap - salt water - and it flows THROUGH the tubes - why else would you need to rod them out unless they were blocked by salt crud. If it was engine coolant INSIDE the tubes - no crud.

The exchangers on your 120 work in exactly the same way, The
zincs go into one of the end chambers (salt water)
Cheers

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Old 10-25-2015, 07:59 AM   #8
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Quote:
Originally Posted by Brisyboy View Post
Mike,

Fear not- the raw water enters the cooler at one end, passes through the tubes then exits at the other end to move on to cool the transmission oil via its own heat exchanger then ultimately into the exhaust to cool that too. If you will excuse the pum, the poor sea water must be exhausted by the time it is spat unceremoniousyl out the exhaust . The exchanger is divided into three separate compartments; the ends, where the raw water enters (in one end), and exits out the other. and the larger centre section where the coolant circulates around the outside of the tubes.
The two end chambers are connected by the tubes through which the raw water passes . The coolant circulates through the centre section and gives up some of its heat to the cooler raw water that is passing through the tubes. The raw water and coolant are totally isolated so taking off the caps at each end will just allow a little raw water to escape. Not too much. Don`t forget to close the sea cock although the heat exchanger is probably above the water line.

cheers

Thanks George. That is what I thought, but wanted to confirm before I dumped a bunch of new coolant out.

Mike


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Old 10-25-2015, 09:04 AM   #9
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So, are the zincs into the raw water or the coolant. To me, the latter makes no sense, as the coolant has anti-corrosive in it anyway. If into the raw water chambers, which makes more sense, being salt water to boot, the placement in relation to the tubes is hard to picture.
Obviously the zincs are immersed in salt water. You need to take a good look at your heat exchanger and find the raw water inlet/outlet, the coolant inlet/outlet and open the end cap where the zinc is located to get a true picture of how it works.
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Old 10-25-2015, 02:06 PM   #10
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All was as Brisyboy described. Removed end caps. Only salt water came out. There was some debris on the inlet side, but I cleaned that up and everything is back together. Thanks for the help.


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Old 10-26-2015, 07:52 AM   #11
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Ok, I get it now. Thanks for clearing up a misconception I was under. I guess I just envisaged it being the other way round, as from a design and efficiency angle, the coolant in the tubes, and the higher flow of the raw water in the outer chamber seemed to make better sense. But hey, what do I know..? Must be some other reason I haven't thought of.
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Old 10-26-2015, 10:22 AM   #12
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At the suggestion of a more experienced mariner, I marked the end caps to align with the body of the exchanger (magic marker). Also allowed different markings to be sure to but them back in the same orientation (fore and aft). I don't know if this is truly needed, but is not difficult to do. I found a couple of old zincs sitting in the forward part of my exchanger.
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Old 10-30-2015, 08:13 AM   #13
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Well, after all the great discussion, I thought this thread had been put to be.....until............I was sitting in the engine room - as you do - idly following the passage of raw water through the cooling system - after the discussion re exchangers/coolers having three compartments with the raw water entering at one end, passing through the tubes and exiting out the other end, all was going to plan until I looked at the main heat exchanger for the engine coolant - something didn`t fit, I know it has three chambers, I know each end is salt and the middle coolant BUT the raw water enters and leaves from the same chamber - the rear one - huh - how does it pass through the tubes to take the heat from the coolant if it enters and exits from the same end - I even took the rear plate off to check that there wasn`t a tube that directed the incoming water to the forward compartment - nothing that I could see.

So, how does it work. - Unless I am missing something, there is no through flow of cool raw water.
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Old 10-30-2015, 09:29 AM   #14
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Well, after all the great discussion, I thought this thread had been put to be.....until............I was sitting in the engine room - as you do - idly following the passage of raw water through the cooling system - after the discussion re exchangers/coolers having three compartments with the raw water entering at one end, passing through the tubes and exiting out the other end, all was going to plan until I looked at the main heat exchanger for the engine coolant - something didn`t fit, I know it has three chambers, I know each end is salt and the middle coolant BUT the raw water enters and leaves from the same chamber - the rear one - huh - how does it pass through the tubes to take the heat from the coolant if it enters and exits from the same end - I even took the rear plate off to check that there wasn`t a tube that directed the incoming water to the forward compartment - nothing that I could see.

So, how does it work. - Unless I am missing something, there is no through flow of cool raw water.
The two paths of the raw water are divided from each other in the chamber where the inlet and outlet are located. The incoming raw water flows down one side of the heat exchanger to the other end of the tubes and then back down to the outlet.
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Old 10-31-2015, 05:12 PM   #15
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The two paths of the raw water are divided from each other in the chamber where the inlet and outlet are located. The incoming raw water flows down one side of the heat exchanger to the other end of the tubes and then back down to the outlet.
Thanks Capt Bill - - you are 100% correct - my curiosity got the better of me and after your post I went and took the rear plate off - sure enough a baffle divides the compartment and I can see now how the raw water goes through half the tubes to the front then back down the other half and on to the next cooler. I guess I missed the baffle because it was hidden behind one of the cross braces.

Another piece of the jig saw added - thanks again
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Old 10-31-2015, 05:53 PM   #16
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Thanks Capt Bill - - you are 100% correct - my curiosity got the better of me and after your post I went and took the rear plate off - sure enough a baffle divides the compartment and I can see now how the raw water goes through half the tubes to the front then back down the other half and on to the next cooler. I guess I missed the baffle because it was hidden behind one of the cross braces.

Another piece of the jig saw added - thanks again
Your welcome.
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