Heat exchanger failure

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Veteran Member
Apr 3, 2013
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Bristol 42
We were taking our boat out to run the engines on Monday, I just throttled up once the engines were up to temperature when my bilge alarm sounded continuously. Turned out the end casting with seal and cover attached had blown off my Stbd Engine heat exchanger (Lehman 120) and we were pumping raw water into the engine room.
No real problem, just had to shut the engine down and get back in our slip on one engine.
It seems a strange failure mode to me, the pencil zinc was situated right next to this end and was fairly new, maybe the soldered joint has corroded away and failed, there is no obvious corrosion to the cast ring just some calcification.
Does anyone have any ideas?
Thanks, Steve


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When was the last time that heat exchanger was removed and cleaned out?
Cleaned thoroughly about 2 years ago and checked regularly for build up since.
Mr. Sk. Looks to me that the soldered edge has given up the ghost. From picture #2, it looks like the end cap is still attached (bottom most piece against your thumb) then the rubber gasket, THEN the thicker piece that should have stayed on the HE. That thicker piece should be soldered to the HE and failure of that solder joint is the cause of the blow-out. Absolutely no evidence of solder so this is NOT new development. Best suggestion I can make is take off the HE and either do it yourself or have the cap soldered back on. Not sure if OEM was soft (lead) or hard (silver type) solder.
Isn't there supposed to be a bolt in the middle of that cap to hold it on? They are supposed to be removable for cleaning...I thought...
Mr. X. I think the pictures are of the cap AND the fitting it bolts into (shown upside down) with the bolt on the bottom side. The whole smutz has let go.
My question is, “How old is the heat exchanger”? They have a finite life. We’ve been told to change them every 10 years, even if they pressure test ok.
Solder failure. Did you get any freezing?
No no freezing, the casting you see goes into a recess in the end of the HX main tube, as RT says it looks like the solder has failed. I will pull it at the weekend. I plan to grit blast the mating faces to get a better look and maybe re-solder it for a spare. In looking further I have noticed that there is no ground bonding cable on that engine so maybe that has contributed. although I have regularly checked and changed out the HX pencil zinc.
I would have thought that the zinc still would have been sacrificed rather than the solder but maybe someone can advise me on that.
I will install a grounding cable to be certain.
I'm not sure how long the HX has been on there, I have had the boat nearly 5 years though, might see if I can contact the PO but should probably fit a new one to be safe.
Does anyone know the most economical place to order a new one, I'm in Panama City, Florida.
Thanks, Steve
Mr. Ske'. Is the HE in question mounted directly to the engine by means of a soldered on bracket or is it mounted by means of non-metallic stand-offs? If non metallic stand-offs, for sure you will need a grounding strap.

I have no idea what solder was used to affix the tubing bundle to the outside housing BUT if soft solder, you will have to heat-sink that bundle/housing joint when you reattach the end casting. I suggest submersing the HE in water up to that bundle/housing joint to protect it's integrity. You should then have about 1" to 1 1/2" of the HE sticking out of water to solder to.

American Diesel and Bomac are the only two sources of OEM coolers I know of BUT I have seen reference to generic suppliers suggested by other members. As per usual, I can't remember squat...
I had this happen, although only to a leak, and not a blowout.

Turns out lead/tin solder is attacked by chloride from seawater.


Sandia Labs figured this out a number of years ago.

This is not a cleaning issue, and maybe even not a lack of zinc issue.
had the end cap of a oil cooler fall off one day...

never looked like any solder was even used, but was on there 5 years.

5 years was when we changed them out on the assistance tow boats.
Thanks to everyone for the posts, RT, I had thought about filling the HX with water to protect the inner tube joints during soldering but immersing it also should be even better, thanks. I will check the mounting and bonding

Diver Dave, I have always maintained a good pencil zinc in the HX, the article you posted is interesting if a little over my head, you would think this would be a more common problem if it were just a salt water corrosion problem

The faces on the casting that blew off look clean (once cleaned off with a wire brush) with no trace of solder, if they were tinned properly you would think that there would be some indication of the solder in the surface of the brass. I'm assuming that a lead/Tin solder is used rather than a Silver solder?

I've just sand blasted the casting and still no sign of solder, see pics.

I am a little concerned that the soldered joint on the smaller internal tubes are being affected by the same phenomenon so i think I will have to bite the bullet and buy a new one (as cheap as I am!). I'm just wondering about the other engine HX now!

Thanks again Steve


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The Table 2 in that study points to the chart of active vs non-active alloys to use. We think of lead being fairly non-reactive, but with seawater and CO2 attack, the lead portion of the solder is simply slowing going away. It is combining with Chlorine and leaches away.

Think about brazing the caps back on. I've not done a ton of brazing, but did do some using a copper alloy rod on copper fittings.
In your case, you want to inspect carefully the tube joints to the separator plates. These SHOULD be done with a higher melting point solder (or brazed) than the case and end caps. Otherwise, the heat required to pull off the end caps would disassemble the entire heat exchanger, tubes and all!
If they look good, I would certainly explore brazing the end spiders on. It might not be repairable in the future, but you could squeeze out quite a few more years out of them.
Sea Kamp, cupronickel heat exchangers for the Ford Lehman's are readily available for less than $700. I'd buy new and not mess around. When we changed ours out, we also changed the transmission and oil coolers. Less than $250 for the pair.
Sea Kamp, cupronickel heat exchangers for the Ford Lehman's are readily available for less than $700. I'd buy new and not mess around. When we changed ours out, we also changed the transmission and oil coolers. Less than $250 for the pair.

I think this is really good advice. Any mess up or leaks could put salt water in places it really shouldn't be, and cause significant damage.
Better to replace the whole unit. Have old one replaced and carry as a spare. They care expensive. Contact American Diesel if you have questions.
Also, if you replace oil coolers get larger capacity after market coolers from American Diesel.
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