I've driven around in 40-odd degree days, and I've got one of those chinese alloy radiators and 4 spotlights!
Seems okay.

I've also got one of the Chinese alloy radiators and temp gauge doesn't go over 85 degrees, even on a 42 degree day.

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1963 Morris 850

I once drove my hotted up Cooper S from Adelaide to Melbourne in 37C+ heat often hitting 80-90 mph on the long straight stertches (it was 1978). Black paint too but at least it had a sunroof. No thermo fan, just a four blade and Moke California radiator fitted. Sure it got rather warm but it did not boil and kept going the distance without any problems. Aircon was unthought of in a Mini back then of course.

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

My 1275spi mini is great in hot weather. With air con on you hear the thermo fan kick on and off but temp gauge never goes over 1/2 way as normal. Our other 998cc rover with air con is fine up to about 35degrees, after that with the air con on the temp gauge moves up to just under the red. That's with the new alloy radiator as well as the thermo fan.

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88 Rover 1.3i "Reggie"
99 Rover 1.3i “Grover”
12 Mini Cooper S "The shitter"
17 Mini Clubman JCW “Noddy”

My 850 runs fine in the heat but the after-boil is annoying.

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Behold! The mighty 850!

Iv used my van as a daily driver for 6-7 years in perth its std with no thermo fan. I have added an expansion tank which does help. I also live up the hill so it gets a hard time in summer but had no dramers with it just dont forget a towel for yer seat:)

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66 Van 1275
69 K Sedan
69 K Van Teabag
66 austin Countryman
68van

yeah I took it on a tour yesterday in 41 degree heat and the gauge moved up a bit, however I was constantly on the move.
In peak traffic with bumper to bumper cars and crawling along, there is no way it could withstand being out there for so long the way it currently is.

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Matt

A while back my brother told me that the temp gauge was sitting higher than it used to. It didn't boil, but it usually sat at 1/3, now it was 3/4. Then on a ~35 degree day, it overheated and he had to limp it home.

Turns out the crank pully had shattered - the fan wasn't even turning! On cooler days it still seemed to do OK.