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Heat Exchanger Repair

CaboJohn

Regular Contributor
I have twin 2002 Captain's choice 5.7 engines. The port side has had the “missing coolant” symptom for a year or more that has varied in intensity but is getting worse. Nothing in the bilge or oil. I will return to the boat (in Mexico) next month to attempt a repair. I have some new stuff (florescent tracer fluid and hardware to pressurize and measure pressure changes in the coolant system with the engine off, etc.) that I think will enable me to find the leak. However, I've had an “aha” moment that has convinced me that the most likely spot is the heat exchanger. I will check it all out, but let's assume for the moment this is the issue.


Some time back I had a leak around the nipple on the heat exchanger that provides water to the dripless shaft seals. It seems this was an old problem that the previous owner had fixed with JB weld or some similar material. I took the exchanger to a welding shop and asked the owner to braze on the nipple. After several hours of failure he delivered the part with a poor looking braze and said the solid copper body had prevented him from getting it to the necessary temperature for a good braze.


Sure enough, on installation I bumped the part and it fell off. I next decided to replace it with a threaded connection. Using a couple of rubber gaskets, some curved washers and a nut I quickly made a leak proof, no heat required fix. Live and learn.


Now I believe I have an internal leak in the exchanger. Perhaps when he heated the shell to attempt a braze, he also caused the joint between the shell and internal tube wall that separates the fresh from the salt sides to lose it's solder and start to leak. Assuming this is correct (and I can find it), the issue is whether repair is possible and if so, how?


I am thinking that with a torch on the outside of the shell, and at the last minute another heating inside on the edge of the wall, I might be able to flow low temp solder (63/37, 371F) into the joint. I don't know what the orginal was soldered with, but he must have gotten it to over melting temp to get it to flow out.


Any suggestions or cautions? Would the low temp required make it possible for this to be a DIY with propane or MAPP, or will I need to take it back to the welding shop? Is a rosin core solder likely to work or do I need some other flux? Is a lead/tin joint a potential corrosion issue? Is this whole thing impossible unless I can clean the joint first (I can't)? Lot's of unknowns but the one thing I do know is the high cost of the new heat exchanger!


Thanks for any help.


CaboJohn



 
I could fix the exchanger, I doubt you can.
If you're loosing coolant and it's not in the oil or bilge it's usually the exchanger. It's possible to loose it thru a head gasket. You can pressure test the exchanger to verify the leak. A radiator shop is better suited to repair a heat exchanger than a welding shop. At this point, a replacement exchanger could be cheaper. Lots of companies on the web make replacement exchangers. Here's a few:
http://www.orcamarine.com/
http://www.seakamp.com/
https://www.ejbowman.co.uk/products/MarineHeatExchangers.htm
http://inetmarine.com/CrusaderHeatExchanger.aspx
 
@ Lepke
I tried to explain what I would try to do and asked if anyone knowledgable had suggestions. Obviously I am not sure it will work. You say you could fix it. Could you share how you might approach the problem?

Thanks for your help.

CaboJohn
 
John:

Don't have access to my library right now so details will hav to wait a few hours.....if its a tube (or two or three), its usually easier just to block them off. A real torch (twin bottles) works easier but you have to be careful to avoid overheating. solid copper is no excuse for a poor braze - he didn't know what he was doing.

If the entire end of the tube bundle was disturbed, a radiator shop may be faster in the long run....but if they don't know what they are doing, you'll wind up replacing it....
 
Mark,

Thanks for the response. There was not evident corrosion when I last looked inside so I doubted I had a leak until I remembered the attempt to braze. I agree he did not know what he was doing but he did dump a lot of heat in the shell (from the outside) in the process. That's what makes me think he caused the leak. I don't expect to find any radiator shops down there. Everyone just replaces or gets a junk one now.

I have been reading about fixing copper radiators in heat exchangers. Looking at things like old car and tractor forums, I see some success using epoxy fixes (JB Weld, etc.). I'm thinking if the leak is in the seam where the tube support wall was soldered to the outer shell then that would be a perfect location for a epoxy fix. And a tough location to solder, particularly for a beginner, given the heavy outside shell that needs to get to solder temperature. I could get at both sides of the seam to really clean it well (but not in the seam where the solder needs to flow) so the epoxy would have a chance of making a strong bond. Worth a try?

John
 
John:
there was nothing regarding repair in the crusader literature I have.

the Mercruiser manual says you can close off up to 3 holes, if they are leaking, and suggest brazing (BCUP 2 rod) or silver soldering.

I can tell you I've fixed more than one oil cooler by reassembling it with 95/5 solder. I'd suggest a mild acid flux with a muratic acid wash to prep the joint.

if you'd rather go the epoxy route, I'd think the acid wash would still be reasonable....followed by a water rinse and a thorough dry before trying to seal it.
 
John, we staved off replacing both HEs for our 8.1s for several years by doing what someone else here suggested and that was blocking off leaking exchanger tubes as we found them. We first rigged up a setup that allowed us to pressure test each HE, watched for bubbles, id'd the tube then blocked it off at both ends. we found that using a .17 cal cleaning brush got the inside of the offending tube (and all the others for that matter) clean enough for a bit of 5100. worked every time. Our HEs were shot but we were able to maintain temps with up to 4-5 tubes blocked off. Of course we are in Cape May, NJ and not Mexico. BTW, we had to break the cooling system down into sections for pressure testing purposes. The whole project was quite the learning experience. Good luck with yours.
 
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