When reading a pressure-temperature chart for an engine cooling system, what should be compared to spec?

• A. Only read the temperature; pressure is irrelevant.
• B. Interpret the chart by comparing to air temperature.
• C. Compare measured coolant pressure and temperature to spec; ensure pump, cap, and thermostat maintain proper operating ranges.
• D. Use the chart to set valve lash.

Answer: (C)

Comparing measured coolant pressure and temperature to spec is how you verify the cooling system is operating within its designed limits. The chart defines the expected relationship between pressure and temperature in a healthy system, and the pump, cap, and thermostat are the components that keep those values in the proper ranges. If the readings fall within the specified ranges, the system is circulating correctly and staying within safe limits. If either value is off, it points to a potential issue with one of those components or with coolant flow, which could lead to overheating or overpressure.

Other ideas don’t fit because relying on temperature alone ignores pressure effects, using air temperature as a reference isn’t meaningful for engine cooling, and valve lash is unrelated to the cooling system’s pressure-temperature behavior.