Engine Fire Extinguisher System - An Engine Fire or Overheat is monitored in four sections of the engine. In each section there are two sense loops (A and B) containing a gas. If the temperature rises the gas pressure increases. If the pressure falls to zero due to a leak then a FAULT is sensed. The difference between an Overheat and Fire is the temperature at which it is triggered: Overheat/Fire 1) Upper fan case 174C/304C 2) Lower fan case 174C/304C 3) Left core 343C/850C 4) Right core 343C/85