Consistency of semen, much like the volume of the load, is highly dependent on the amount of time since a guy's last orgasm and how long he has been stimulated in the current session. If a guy comes too often, his body doesn't have the time to slowly regenerate ejaculatory fluid and thus his cum is often very thick. This won't be the case, however, if the guy has been aroused for a while prior to coming since his body produces the fluid at many times the resting rate when he's erect. Therefore, if he's come several times in the last day and he comes within a few minutes of getting aroused, his cum will sort of ooze out very slowly... but if he comes after 30 minutes or an hour of stimulation, it will gush like water.