Heat Exchanger Pitting...how big a deal is it?

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G

goletamoby

Member
Joined
Dec 2, 2022
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20
Fluid Motion Model
R-21
Vessel Name
Nomad
During engine servicing, corrosion was found around the heat exchanger's end cap. When we opened it up, they found some pitting.

https://drive.google.com/file/d/15FS7Xa ... sp=sharing

The mechanic is suggesting the replacement of the entire unit since individual parts are apparently no longer available for this model.

My question is, how urgent of an issue is this, and is there something we can monitor to tell when it would be time to do something?

Nomad is a 2014 C-26.
 
Have you owned the boat since new or did you buy it used? Does the boat live in a slip or is it trailered? From your explanation it sounds like you noticed external corrosion is that correct? Or did you open it and then found corrosion?
 
Bought used, lives (and lived) in a slip. We noticed corrosion around the seal of the heat exchanger, that’s why we opened it up.
 
Whether it needs to be replaced kind of depends. No need to replace it if the mechanic is willing to put it back together with RTV on the sealing surfaces and if you are willing and able to flush the engine after you use the boat and to periodically check/change the engine zinc. The only way to monitor it is to watch for it to start leaking again. If you just want to use your boat and walk away from it at the end of a cruise then have it replaced and it'll likely last another nine years.
 
Thanks, Dan. Is there a recommended procedure for flushing the engine? I’m more than happy to do whatever work is needed to keep it in as good of shape as possible.

For the moment we did reseal and re-install. So I guess it’s a matter of just monitoring and watching for leaks?
 
If it's possible to pressure test it for leaks I would do that.

If the boat doesn't have a galvanic isolator presently you might want to add one. That would help mitigate any future corrsoion.

-martin610
 
goletamoby":7hm0hkls said:
Thanks, Dan. Is there a recommended procedure for flushing the engine? I’m more than happy to do whatever work is needed to keep it in as good of shape as possible.

For the moment we did reseal and re-install. So I guess it’s a matter of just monitoring and watching for leaks?
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Flushing with fresh water is pretty simple. Close the seacock, take the top off the raw water strainer, stick a water hose in the raw water inlet and run the engine for a few minutes. Put the top back on the strainer and leave the seacock closed until next time you run the engine.

Some people install a fitting to attach a hose to the system without needing to open the strainer. That's OK for flushing on the trailer when you can leave the seacock open to avoid over pressuring the system. I'd not recommend it for flushing in the slip.

Until you establish a history with the boat I'd monitor the engine zinc periodically. Maybe check it once a month and take a pic of it. Compare deterioration vs engine operating hours. Try to get a sense of whether the zinc is active sitting in the slip or only when running in salt water.

The existing corrosion damage may have been due to the prior owner not flushing(most people don't) and/or not maintaining the engine zinc. Or it may simply be the nature of the beast. But I'd be surprised to see damage if both flushing and maintaining the zinc had been done. What you're seeing there is known as "crevice corrosion" which occurs as the name implies in confined areas where there's poor fluid circulation. That's why the pitting is confined to that small area. So when you flush the engine it's important to give it long enough to fully flush the salt water out of those spaces.
 
Interesting, makes a ton of sense. Thank you!

When flushing, how important is it to get the hose flow correct? Seems it could be tricky to match the flow of the engine pump. And any idea how long it might take to flush the whole system?
 
goletamoby":35szwo19 said:
Interesting, makes a ton of sense. Thank you!

When flushing, how important is it to get the hose flow correct? Seems it could be tricky to match the flow of the engine pump. And any idea how long it might take to flush the whole system?
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It's not super critical to match the flow rate. At typical city water pressures a hose will likely supply more than the engine needs at idle. You can tweak the faucet a bit to match the engine demand if necessary. If it overflows the strainer the bilge pump will activate so make sure your bilge is oil free. If flow isn't keeping up with the engine demand it's no big deal for idling a few minutes. As long as you've got some flow the impeller won't be damaged and you can monitor engine temperature. We have poor water pressure at our house and the hose can't quite keep up. Not an issue.

I'd run it five or ten minutes. You want to get the salinity down as low as possible.

It's a bit of a hassle having the engine hatch open while doing this. On our R25 classic I ran a hose through under the rail, cut it to length, and secured it with wire ties along the route. One end lies beside the strainer when not in use and the other end tucks up under the rail out of the way until needed. The end in the engine room has no fitting on it and is easy to stuff into the port inside the strainer so it's shooting right into the inlet to the pump. The other end has a standard female garden hose fitting. Fitted like this once you get everything running and faucet tweaked back if necessary you can close the hatch and be scrubbing the boat or whatever while it's flushing. Just keep an eye on it.
 
NorthernFocus":28tfab2z said:
goletamoby":28tfab2z said:
Some people install a fitting to attach a hose to the system without needing to open the strainer. That's OK for flushing on the trailer when you can leave the seacock open to avoid over pressuring the system. I'd not recommend it for flushing in the slip.
Click to expand...
Click to expand...

The trick to this is to just flush it with the seacock open. Fresh water is lighter than salt water, so it will float, I turn the hose full blast and will get bubbles out the side of the boat with the engine off when I start this process - so I know that water pressure is flowing backwards from the strainer to the sea (and not turning the impeller and filling up the muffler lift). I'll then turn the engine on and keep the water full for 5 minutes or so before turning off the engine, running the hose for another minute or so, then turning off the water, and then closing the sea cock.

Maybe some salt water does stay in the system this way, but the risk of running it dry with the cap off the strainer method (and the hose jumping out) is larger in my mind than a bit of salt.

I have my steps listed here - viewtopic.php?f=24&t=20427
 
Awesome ideas, thank you both!

Final dumb question...how do I find the engine zinc?
 
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