What are the potential consequences of running an engine without coolant?

Running an engine without coolant can lead to overheating and severe damage, which is why this is the correct response. Coolant plays a critical role in maintaining the engine's operating temperature, preventing overheating by dissipating heat that is generated during combustion. When an engine operates without coolant, it cannot effectively regulate its temperature. This can cause the engine to overheat rapidly, leading to a range of serious issues such as warping of engine components, blown head gaskets, and potentially catastrophic failure.

In contrast, the other choices do not align with the realities of engine operation. Increased fuel efficiency and enhanced engine performance typically rely on optimal operating conditions, which include proper temperature regulation facilitated by coolant. Similarly, improved lubrication is contingent upon the engine running within its intended temperature range. If the engine overheats, oil can break down and lose its effectiveness, hindering lubrication rather than enhancing it. Thus, the consequences of operating without coolant are mainly detrimental and result in extensive engine damage.