Some of my own "Laymans" thoughts for what their worth.
Iv'e not seen any comments regarding overheating/running hot on the gauge in any road tests of the time when these cars were new/er and would have had healthier cooling systems than many current classics of today (though of course the ambient temp may well have been average on the test days).
Was there any hearsay around at the time these cars were everyday (but not too old runners) about them being prone to overheating?.
Lots of them would have likely to have been stuck in say holiday jams on hot days at some point.
Well, we were a Triumph family back in the day when you could buy Triumphs new.
Between the old man, me and my brother…
Toledo, Dolomite 1850, Dolomite Sprint, 2500pi, Herald 1200, Herald 13/60, GT6.
Other than my Sprint which was a law onto itself, none of them were particularly problematic with overheating, certainly no worse than any contemporary.
The Sprint? That managed to overheat when it was -13 C outside!