Oui ..yes, Yves, I replaced what you call a ‘calorstat’ and what I call a ‘thermostat’ ..same thing, I think.
That was the 1st thing I thought of when the engine was overheating, so I did change that by removing the fresh-water header tank, and – on my engine – the ‘thermostat’ is directly beneath that header tank. (I may have replaced it twice in 12 years, I think.) After changing the thermos it’s easy to replace the fresh-water header tank ..just two bolts, I think.
I also checked the fan belts – to make sure that the raw-water pump was pumping properly! – and checked the raw water strainer ..the whole water system, in fact. The problem was the clogged engine cooling heat exchanger. When I’d removed all the old junk inside it, and cleaned out the narrow copper tubes with a SOFT, WOODEN, LONG-HANDLED artist’s paintbrush handle, everything ran perfectly and cool again.
Thanks for asking!