In the published version, the fur coats have been omitted, doubtlessly in view of the heat. Again heat comes into the picture before they can leave. Daisy suggests that they should smoke a cigarette before leaving. Tom says they did that all through lunch. As they board their cars, Daisy suggests that she and Gatsby follow the others in Tom's car.
Heat plays another important function.
Tom says he's probably got enough gas to get to town but Jordan objects. Thus, Fitzgerald has provided a believeable reason for stopping at the garage, a reason in keeping with his characterizations. The unmitigating heat adds tension to the upcoming confrontation but it also delays the action so that the confrontation scene can be more fully exploited and believed. Just as heat represents the building up of emotions and losing of control, cool represents control. Nick remembers vaguely the argument that occurred at the Plaza.