Well, it's been a VERY long time since I did any time trialing, but the steady exertion is pretty similar to running. Under those conditions I'm just going to get nauseous, personally, and as long as I neither bonk nor pass out from the heat I call it good. But there's a lot of good research behind pre-cooling, especially for a shorter event. (20K? 40K?) The idea is to cool your body any way you can before the event, including by drinking supercooled water (slushie or shaved ice). You could bring some in a cooler, and also toss some wet shirts into the cooler to wear before your start. Practice on a non-race day so you know how to avoid brain freeze and muscle seize.