A B737-800 Captain and First Officer report the left engine overheat light illuminated at approximately 60 knots on two separate takeoff rolls; requiring rejected takeoffs. Maintenance found bleed duct disconnected and 12-14 insulators for the overheat detection circuit melted.

Narrative

At ZZZ; Left Engine Overheat light illuminated at approximately 60 kts on takeoff roll just after takeoff thrust was achieved. Captain rejected takeoff and light went out. Returned to gate. Maintenance indicated they found a bleed line disconnected and 12-14 insulators on the overheat detection circuit had melted. Maintenance reattached bleed line and replaced the insulators. Attempted another takeoff. Overheat light again illuminated at same point in takeoff roll. Captain rejected takeoff at about 60 kts. Returned to gate and aircraft taken out of service. Callback conversation with reporter revealed the following information: Reporter stated that after the first rejected takeoff of the B737-800 and maintenance finding a bleed duct disconnected and 12-14 insulators melted for the overheat detection circuit; he and the Captain were quite surprised to see the same overheat light illuminate again; during the second takeoff attempt. Especially since the ground test procedure for the fire/overheat circuit passed; after the repairs had been made. He does not recall if a 'fault' light also illuminated at any of the two times the overheat light illuminated. Reporter stated the bleed duct that maintenance found disconnected after the first rejected takeoff was on the left side of the engine near the compressor case and the overheat circuit was on the upper side approximately in the mid to aft section of the engine. Reporter stated that after the second rejected takeoff; he was told by Maintenance Control that maintenance decided the engine would most likely be changed.