The Los Angeles Marathon was a death march! The temperature at the start was in the lower 80s and climbed to 90 by the time I finished the race. Many people suffered from heat cramps and vomiting, and had to be pulled off the course. But I did NOT suffer from any of those problems, which was probably due to the high sodium content of the e-Gels I ate during the race; I ate 5 of them!
I have used e-Gels since then on all of my long runs, and they have helped me during the hot weather runs.