Last week I ran Rydlyme through the engine's (Yanmar 3JH) salt water
passages, including the heat exchanger
and I thought you might like to know how it worked.
had never been treated (10 yrs old).
It was in there for three hours, the first two with a circulating pump, the last without ( the pump quit).
Afterwards, on removing the end caps from the heat exchager it was clear that the tubes in the exchanger were beautifully clean, except for one little area where there must have been an air bubble.
One of the end caps still had two clumps of calcification that had not responded to the treatment and this was a little disappointing, as if it had subsequently broken free, some of the tubes could have been blocked, negating the cleaning
I would suggest that it is well worth using something like this, but you should still pull things apart to check afterwards.