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
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