Engines get very hot operating anywhere. The problem with using the 0w-40 is the way the hybrid engine turns on and off. If the oil has reached the 40w and has not cooled enough to be the 0w (or5w) again then when the engine restarts periodically the oil can't pump up fast enough. My recommendation if you are concerned about extreme summer driving is the 5w-20 because it starts out a little thicker but that's okay because the ambient temperature keeps the engine warm enough even when the engine is off in the summer. The advantage is that it doesn't get so thick it can't pump rapidly when needed.