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Old 10-08-2019, 07:27 AM   #1
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Heat Exchanger Lehman 120 - When to Replace

First, I searched and searched and was unable to find a definitive answer as to how many years of use before a heat exchanger should be replaced. Yes, I am aware that they can be cleaned and pressure tested. But, here is my concern with pressure testing even if I could find a local shop that still offers this service.

So, the unit is tested and it holds pressure but how can one possibly know how close the unit is too blowing a hole somewhere? In other words, integrity may be marginal, on the edges of failure, with no way of knowing that it is marginal because the unit holds pressure at the moment of testing. So, given this premise, that pressure testing is of dubious value, how many years use before replacement? I am guessing that I will get many anecdotes which can be valuable information. Unlike oil coolers, these are not inexpensive items. My boat is 36 years old and maintenance records (incomplete) do not show that they have ever been replaced. I have already replaced the oil coolers.
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Old 10-08-2019, 07:37 AM   #2
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1 am just getting ready to change the coolers on mine. They are known to be 12 years old. With (I am guessing) 1,000 to 1,500 hours. This is preventative maintenance. Maybe premature however when we purchased the boat a year ago I found 0 zinc left. Brian at A D diesel says 1500 hours........I think. I am of the belief that hours are not nearly important as time in salt water. The new ones are the copper only, painted up and ready to go. As I said, maybe premature but it does afford a piece of mind.
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Old 10-08-2019, 07:42 AM   #3
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If the coolers are well flushed with fresh water on a yearly basis before being laid up for winter (here in the northeast) I am of the opinion that they will last much much longer.
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Old 10-08-2019, 08:06 AM   #4
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Are the tubes copper? Cupronickle will last twice as long and only costs a little bit more.


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Old 10-08-2019, 10:32 AM   #5
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The past history of zinc replacements would be a better indicator of lifetime, if it exists. Most of us have not owned our boats for their whole lifetime, so such records are rare. Those of us who have owned our boats a long time risk fading memories or, early errors ie failures to follow best practices early in our experience.
With good cathodic protection, even (especially) in salt water, engine HEs, transmission coolers and engine oil coolers should last a very long time.
Recommendations by AD will be based upon the presumption that no previous records exist and the fear that no proper cathodic protection was provided for much of the first 1500 hours.
Inspection helps, pressure testing helps, but only your personal comfort level can make the final determination.
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Old 10-08-2019, 10:39 AM   #6
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Quote:
Originally Posted by djmarchand View Post
Are the tubes copper? Cupronickle will last twice as long and only costs a little bit more.


David
I went with copper based on Lenco and ADís thoughts. Maybe self serving? Copper seems to offer better heat transfer. As mentioned above fresh water flush and monitoring of zincs will greatly extend the life. Hereís hoping.
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