BLUEMOMENT

DaveS wrote:On a more satisfactory topic the HCl in the boat engine jacket was very effective: 10 minutes of vigorous fizzing then lots of crud came out as it drained off. Overheating appears to be cured. I think it might be worth doing this as a precautionary measure every few years.

It may not be necessary now you've got it clear Dave. The problem can be a form of 'thermal runaway' where overtemp begins to cause the salt to precipitate, narrowing the galleries, which causes more overheating etc. As long as the thermostat is correct and working, the design should keep the salt in solution.