CAT Aftercooolers — and whats Real

In your boots, I'd take the opportunity to install also a fresh water flush connection.
It was discussed in this thread, from post #40 onward.
God only knows by how much it will lengthen the life of your CACs (and also of other bits), but pretty sure it won't hurt.
All the lake boats out there are a living proof that boat engines are happier to live in fresh water...

U R welcome, I hope it will prove effective for you.
It certainly did for me so far, though with different engines.
But the principle is valid in general, and possibly even more with Cats, considering their recent coolers history.

I'm not saying that your theory is wrong, but it's not like Cat is alone in that design.
In my 17 years old MANs, whose CACs are also on top of the engine, they were never replaced.
And based on how they looked when stripped and cleaned a couple of years ago, I would expect/hope them to do their job for many more years - though I'm saying this with my fingers firmly crossed, of course.

Btw, my last boat before the current one was Cat 3116 powered, and even if those engines certainly aren't among their best ever, they are still working just fine now that they are 26 years old, and with their original coolers.

I mean, it's not like we're talking of rocket science here.
In fact, I'm wondering how long it will take before someone will put together a class action against Cat on this issue - unless someone already did and I missed it, maybe...?

The 3412E didn’t have the issue. The ones I ran were 13 years old and had 5500 hours when the boat sold.

My point exactly!

That’s why I feel the recommendation for the upgraded design is just a legal CYA. The few car specialists I talked to agree.

they re like the C32s and I think all other modern cats. Closed cooling system with seawater in the HE, AC, gear and fuel cooler etc

the 3412s has one stupid “feature” ... the fuel cooler is before the raw water pump and catches whatever debris gets thru the strainers... they re easy too clean every year or two though.

I mentioned years ago, To many different formulas in the solder used. Ever notice you can not repair a Cat air cooler? The solder will not puddle smoothly or even mix with any thing we tried years ago.
The assembly vendors flux and drag the air cooler thru a pool of this **** solder. Think of it as older puk metal. Sometimes it last, some times it does not.

Never found a Cat HE or cooler of any kind have a metal issue. Always that F**&&ng solder.

Going a bit O/T now, and I apologize with the OP for this, but you are raising an interesting point.
There is in fact quite a bit of confusion on MAN's anodic protection (or lack of).

The reason why there are no zincs anywhere on the engines is that they are bonded with a large external transom anodes, whose main advantage, arguably, is that it's harder to miss when it must be replaced, compared to several pencil anodes somewhat hidden around the engines.
But this is all well and good, that's the way MANs were designed.

Where in my experience MAN recommendations clashes with the reality (and I guess it's the reason why you are suggesting that their coolers are isolated) is when they suggest that engines should be isolated from the rest of the onboard DC circuit.
I've seen plenty of MAN powered boats, built from several different builders, and in all of them, bar none, the engines were earthed with anything else onboard.
In other words, I've always seen engines and all their bits (HEs and CACs included) bonded with seacocks, domestic DC bank negative, and anything else bonded onboard.

If by chance you would come across a boat where this doesn't happen and engines are fully isolated, I'd be curious to hear who the builder is, because obviously that depends on the installation, rather than on the engines themselves.

All that said, back to the point, yes, no doubt there's something very wrong with these Cat components.
Both the explanations from CR (poor soldering) and BC (aluminum cores) could be valid, but the latter sort of contraddicts what CR said about never having found any metal issues...

Any failures around us has always (when autopsied) been a solder failure.

I don't see much difference between a bonded / non-bonded requirement with MAN engines. Their air coolers have usually drained when not running and when wet, the only stray galvanic currents would be between the engines wet parts. Here is where I hope the alloy air cooler is bonded to the rest of the engine. I'm sure it is just in bolting it down.