Oil filter bypass lt flickering and egt counter flashing upon engine startup. 737-3/4/500

737 classic with EFIS system: If pilot reports about engine OIL FILTER BYPASS lite flickering and EGT DIGITAL Counter Flashing upon initial start up of engine. Particularly it happens when aircraft is parked for long time( about a night duration) in cold environment.Do not worry just let the engine get warmed up and advise the pilot to switch off the engine and then restart as per procedure.
I have faced it many times. Subsequent inspections regarding filter condition and pressure switch and wiring check all found normal.The reason of subject snag is as follows:
Aicraft parked in cold envirnment causes engine lubricating oil to become dense and actuates the bypass switch momentarily off and on upon engine start up. AMM states that EGT digital counter flashing is due to the Flickering Oil Bypass Lite. Flashing stops as the oil filter bypass lite becomes stable. Hense the only remedy to this PIREP is Restart of engine after warm up.
regards Malik Javaid


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