Just came back from snett yesterday......it was 40?
The morning was ok...ish but once you get to after lunch and your reaching peak temperature levels i started having issues. Massive brake fade after about 4 laps of 300 circuit. (thats with track pads/discs/fluid). After that I didnt see much point in being there if all you can do is 4 laps. Most left at lunchtime.
My body was fine although Im in my late 20s if that helps......take a big industrial fan if you can. Toolstation has a 18" floor fan for about ?35.
Drink tonnes of water constantly, sports drinks with electrolytes too. Lucozade/Poweade etc..