Cracked block leads to blowing hoses, expansion tank, etc. the combustion chamber pressurized the cooling system.
listen to what Willy T said. The needle goes to 12 o’clock at approximately 130 degrees and doesn’t rise until 230 if I remember correctly.
I plumbed my coolant temp sender at the output before the thermostat, my gauges (oil temp, oil pressure, coolant temp, and coolant pressure) were marked numerically so I actually knew what the temps and pressure was. That’s when I noticed the the actual temperature relative to the factory gauge.
I clocked the gauges so the temp and coolant pressure needles were at 12 o’clock at proper temp and pressure.
Any time those needles were not at 12 o’clock I knew to shut down.
typically 240 degrees is getting into head gasket failure range.
You should start with a genuine thermostat like jimmy said.