Which sign may indicate an impending engine fire while driving?

The presence of excessive smoke while driving is a significant indicator of a potential engine fire. Smoke emanating from the vehicle can suggest that fluids are overheating, components are burning, or that there is other serious engine trouble. This warning sign should prompt immediate attention, as an engine fire can escalate quickly and poses a major risk to both the vehicle and its occupants. Recognizing this early allows the driver to take swift action, such as pulling over safely and calling for assistance.

While unusual noises and sparking wires can also be critical signs of engine complications and could potentially lead to a fire, excessive smoke is typically a more immediate and visible cue indicative of a fire hazard. Thus, while other options provide important information about potential engine issues, the presence of excessive smoke stands out as the most direct warning sign for an impending engine fire.