Cooling Systems — Raising the Boiling Point in Automotive Radiators Which component of a car’s radiator system primarily allows the coolant to operate at a higher boiling point during normal service?

Introduction / Context:
Engine cooling systems run under pressure to raise the boiling point of the coolant, improving heat transfer and preventing boil-over. Identifying the part responsible for pressurizing the system is a core maintenance and design concept.

Given Data / Assumptions:

• Closed-loop liquid cooling with a radiator, hoses, and pressure cap.
• Coolant is water or water–glycol blend.
• Normal passenger car application.

Concept / Approach:
Boiling point increases with pressure. The radiator pressure cap includes a spring-loaded valve calibrated to maintain a specific system pressure, typically between 0.7 and 1.4 bar above ambient. By holding pressure, the cap elevates the coolant’s boiling point, allowing higher operating temperatures without phase change. It also contains a vacuum (return) valve to admit coolant back from the reservoir during cooldown.

Step-by-Step Solution:
Identify function needed: raise boiling point by increasing pressure.Recognize the device that sets system pressure: the pressure cap.Therefore, choose “pressure cap”.

Verification / Alternative check:
Service manuals specify cap ratings (e.g., 1.1 bar). Raising cap rating increases boiling point by several degrees Celsius.

Why Other Options Are Wrong:
Drain plug: only for draining; no pressure function.Water jacket: provides flow passages but does not set pressure.Vacuum valve: part of the cap, but the pressure function is the key for boiling point.Thermostat: regulates flow vs. temperature, not pressure.

Common Pitfalls:
Assuming thermostat affects boiling point; it affects warm-up and flow path, not system pressure.

Final Answer:
pressure cap