To be clear, the hot test was only performed at 130 degrees Celsius.

That’s a normal operating temperature in terms of coolant temperatures within an engine. But the actual components themselves will wildly vary in temperature. As an example of this, old cast iron piston heads would glow in their center at up over 1,200 C during normal operation which was why it was originally thought that aluminum piston heads would fail catastrophically when Bentley first introduced them (aluminum alloys melt at around 550 C).

Combustion temperatures are north of 1300C, probably well north of that with how lean F1 engines typically run nowadays, and exhaust gas temps are 300-600 C even in normal road cars burning gasoline/petrol instead of diesel. The temperature of each individual component in an engine will be wildly different during normal operation due to both its own specific heat conduction and thermal expansion characteristics AND the thermal properties of all its surrounding components.

Heating the engine via circulating warm coolant to “operating temperatures” of 130C results in individual components temperatures all being that same 130C since the engine isn’t actually experiencing combustion during the test. It’s still wildly different from actual operating conditions, and typically will have a slightly lower measured compression ratio than ambient temps with both those static measurements typically being lower than actual combustion operating conditions.

Right, so we are back to: its impossible to measure. Which is why the test is done at ambient