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Old 05-03-2021, 10:04 AM   #1
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Heat xchanger salting up

Lehman 120. Cleaned and flushed heat exchangers a month ago. New gaskets and zincs.
Ran about 3 hours and checked after sitting 6 weeks and all salted up again. Did I not tighten properly? Previous owner used gaskets and sealer which I cleaned off.

Are there o rings Im missing for the nuts ? Leaking is mostly from zincs. I was afraid to crank down too tight or use sealant.

Please let me know what I failed to do correctly.
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Old 05-03-2021, 10:12 AM   #2
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What does salting up mean- heavy scale on the inside of the tubes or what???

Did you flush with acid? What kind, strength and how long did you leave it in?

Are you seeing a level change in your coolant system?

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Old 05-03-2021, 10:21 AM   #3
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What does salting up mean- heavy scale on the inside of the tubes or what???

Did you flush with acid? What kind, strength and how long did you leave it in?

Are you seeing a level change in your coolant system?

David
David, I’m talking about dry deposits on the outside of the exchanger. Fine bright white salt like mineral deposits around the zinc nuts and around the edges of the end caps. On the outside.
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Old 05-03-2021, 10:25 AM   #4
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The current recommendation is, if you are going to leave the boat for a period of time, give the engine a fresh water flush.
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Old 05-03-2021, 10:38 AM   #5
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I only flushed the inside of the exchangers with fresh water and washed out scale. I did not use any chemicals. I cleaned caps well and reinstalled with new gaskets. All was tight with no leaks. Like I said when I came back in 6 weeks all covered with the fine mineral deposits. Must be leaking.
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Old 05-03-2021, 10:44 AM   #6
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I only flushed the inside of the exchangers with fresh water and washed out scale. I did not use any chemicals. I cleaned caps well and reinstalled with new gaskets. All was tight with no leaks. Like I said when I came back in 6 weeks all covered with the fine mineral deposits. Must be leaking.
If you have it done at a shop, they will pressure test it too.

Is the salt deposit all the round the external heat exchanger?

Guess you will have to sit and watch the heat exchanger when you are running the engine at the dock.
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Old 05-03-2021, 11:18 AM   #7
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David, Im talking about dry deposits on the outside of the exchanger. Fine bright white salt like mineral deposits around the zinc nuts and around the edges of the end caps. On the outside.
Ok if on the outside then it is probably a salt water fitting that is leaking, spraying salt water which when dry leaves a salt deposit. Check carefully for such leaks.


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Old 05-03-2021, 11:41 AM   #8
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Originally Posted by Maravilla View Post
Lehman 120. Cleaned and flushed heat exchangers a month ago. New gaskets and zincs.
Ran about 3 hours and checked after sitting 6 weeks and all salted up again. Did I not tighten properly? Previous owner used gaskets and sealer which I cleaned off.

Are there o rings Im missing for the nuts ? Leaking is mostly from zincs. I was afraid to crank down too tight or use sealant.

Please let me know what I failed to do correctly.
If you are putting an NPT threaded item (the zinc) into a hole with no sealant, it will leak pretty much guaranteed. NPT has a direct path for liquid to follow, right down the lines of the threads, there is no particular sealing surface.

You don't need to be afraid to use sealant. Use an ohm meter and check for yourself. Check it's continuity now with a good quality ohm meter, from it's body to the item it is screwed into. Then install it with some sealant and check again. You'll see for yourself that there is plenty of metal to metal contact to have a great connection, even with some sealant in the threads.

There are articles about this topic. If sealant couldn't be used on NPT threaded items that need to have a good electrical connection, half the sensors on your car's engine block wouldn't work properly with sealant, or they would leak with no sealant.
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Old 05-03-2021, 12:02 PM   #9
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I’ve had good luck using a bit of teflon tape on the zinc nuts. Like mentioned above use an ohmmeter to check continuity.
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Old 05-03-2021, 04:56 PM   #10
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Sorry to disagree but the idea that a leak is pretty much guaranteed is simply not true. I have never used a sealant, Teflon tape or paste, on my FL120 heat exchanger anodes with never a leak. The pressure is not at all very high in the exchanger. And, yes, there is a sealing surface, the tapered threads.
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If you are putting an NPT threaded item (the zinc) into a hole with no sealant, it will leak pretty much guaranteed. NPT has a direct path for liquid to follow, right down the lines of the threads, there is no particular sealing surface.

You don't need to be afraid to use sealant. Use an ohm meter and check for yourself. Check it's continuity now with a good quality ohm meter, from it's body to the item it is screwed into. Then install it with some sealant and check again. You'll see for yourself that there is plenty of metal to metal contact to have a great connection, even with some sealant in the threads.

There are articles about this topic. If sealant couldn't be used on NPT threaded items that need to have a good electrical connection, half the sensors on your car's engine block wouldn't work properly with sealant, or they would leak with no sealant.
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Old 05-03-2021, 05:01 PM   #11
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Same for water temp senders. In fact, some gauge manufacturers specifically recommend against using a thread sealer.
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Sorry to disagree but the idea that a leak is pretty much guaranteed is simply not true. I have never used a sealant, Teflon tape or paste, on my FL120 heat exchanger anodes with never a leak. The pressure is not at all very high in the exchanger. And, yes, there is a sealing surface, the tapered threads.
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Old 05-03-2021, 05:08 PM   #12
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I get salt crystals as well on the outside of my Lehman coolers and have for 15 years. After replacing the end gaskets and checking surfaces, I just gave up on it as it seems to have no real long term effects. I spray vinegar on it once a year and then brush it off.

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Old 05-03-2021, 05:19 PM   #13
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Originally Posted by catalinajack View Post
Sorry to disagree but the idea that a leak is pretty much guaranteed is simply not true. I have never used a sealant, Teflon tape or paste, on my FL120 heat exchanger anodes with never a leak. The pressure is not at all very high in the exchanger. And, yes, there is a sealing surface, the tapered threads.
No need to be sorry, we can agree to disagree. NPT is designed to seal with sealant. The threads are spiral and there is a continuous path for fluids to exit a joint. Here's an engineering white paper on the thread:

https://www.cpcworldwide.com/Downloads/NPT.pdf

With a soft material on one half of the joint, plastic or a soft metal threading into a harder material, I'm sure you can tighten them enough (get the softer material to yield) and get them to have the same effect as putting sealant on them.

There was a prominent marine consultant that wrote a paper and did a study on the use of sealant on threads and I can't remember where it was.

It's very easily measured on your own so you don't have to take anyone's word for it, if you want to use sealant and have peace of mind, do it twice and measure with the meter each time. Very simple.
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Old 05-03-2021, 05:21 PM   #14
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By peace of mind, I meant peace of mind that the sealant is not affecting the electrical conductivity of the joint.
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Old 05-03-2021, 05:52 PM   #15
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I never use any sealant or tape on my Lehman anodes. Just snug them up and done. Never had any leaking issues.
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Old 05-03-2021, 06:45 PM   #16
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You really flushed out all salt from your exchanger? Been there many times and salt just did not wash away no how. I purged the salt from my heat exchanges with a rod.

OK, my above has nothing to do with salt crystals on the outside. I posted only because my experiences with salt were never resolved with simple flushing using all the so called popular cures I could easily get.
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Old 05-03-2021, 06:54 PM   #17
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Greetings,
Mr. M. I don't think you've done anything wrong. Might be previous owners really cranked down on the zincs and distorted the fittings. I would also suggest sealant and checking continuity with a VOM.
Be sure to put a wench on the heat exchanger fitting as well as the zinc nut. The exchanger fitting is only soldered on and can be torqued off if not stabilized with a wrench.
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Old 05-03-2021, 07:01 PM   #18
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Thanks, to everyone who has responded. I have clear path forward.
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Old 05-03-2021, 07:12 PM   #19
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Quote:
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I get salt crystals as well on the outside of my Lehman coolers and have for 15 years. After replacing the end gaskets and checking surfaces, I just gave up on it as it seems to have no real long term effects. I spray vinegar on it once a year and then brush it off.

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Same here. Volvos
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Old 05-03-2021, 07:18 PM   #20
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I always used a sealant on both sides of the edge of the big rubber gaskets on the heat exchanger ends. Otherwise, over time, a little bit of green corrosion began to show. Use a sealant that you can easily pull free. Permatex Ultra Black worked well for me on my two Lehman 120s. That was about the only place I used silicone on the boat - you will hear others literally scream at the mere thought of silicone on a boat for various reasons.
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