What is one key indicator of low coolant levels in an engine?

One key indicator of low coolant levels in an engine is the presence of steam from the engine bay. When the coolant level is low, the engine can overheat due to the reduced capacity to dissipate heat effectively. As the temperature of the engine rises, it can lead to boiling of any remaining coolant, resulting in steam escaping from the engine compartment. This steam is often visible and is a clear sign that there may be a serious cooling system issue, necessitating immediate attention to prevent potential engine damage.

A normal engine temperature gauge reading typically reflects the coolant's ability to regulate engine temperature effectively, so while a high reading might suggest a problem, a low reading alone doesn't necessarily indicate low coolant levels. Similarly, blowing cold air from the heater can happen for a variety of reasons unrelated to coolant levels, such as a malfunctioning heater core or an issue with the climate control system. Frequent stalling of the engine is generally indicative of fuel or ignition system problems rather than coolant levels. Thus, the presence of steam is the most direct and clear indicator of low coolant levels.