When flying single loop operation (MEL) on my 737-300/-400/-500 aircraft, I get a “Fire Warning” light during take-off and climb. What is the cause?

aircraft flying loop MeL operation
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When flying single loop operation (MEL) on my 737-300/-400/-500 aircraft, I get a “Fire Warning” light during take-off and climb. What is the cause?

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A. The most probable cause is a failed detector in the core assembly (P/N 6678). Detectors manufactured prior to 1996 can experience a driftdown of the average alarm temperature, causing the detector to give an alarm condition at a temperature substantially lower that its original calibrated value. Remove and replace the core detector assembly and conduct the “Overheat” average alarm temperature test IAW applicable CMM.