What can cause an engine to overheat?

An engine can overheat when there are low coolant levels because the coolant is essential for regulating the engine's temperature. The coolant absorbs heat from the engine and dissipates it through the radiator. If the coolant level is low, there is inadequate fluid to absorb and carry away this heat, leading to an increase in engine temperature. This can cause serious damage to engine components if not addressed promptly, such as warped heads or blown gaskets.

Regarding the other options: a lack of fuel does not affect the engine's temperature directly, as it relates to combustion rather than cooling. Insufficient oil levels primarily affect lubrication and can lead to increased friction and wear, but it does not directly cause overheating in the same way low coolant does. Clogged air filters can restrict airflow but do not directly cause overheating; their impact is more related to engine performance and efficiency rather than temperature regulation.