dash warning: engine coolant hot

i need some help. i have a 94 deville that keeps displaying engine coolant hot warnings. this has been going on since Feb. I took it to the mechanic and he told me my upper and lower radiator hoses needed replaced. I got that fixed and the warning still came on. I took it back, and they said there was air pockets in the system and they got the air out. for awhile it was fine. then i was cleaning out my car and it overheated. i took it back and there was a crack in the radiator, a fuse had blown and both fans weren't kicking on. i got all that replaced. for while it was fine. then the warning came on again and i took it back and they thought it was air again, and worked on it to get it out of my car. the warning still came on. the mechanic did a block test and everything came out fine. he thought the thermostat might be sticking so i got that replaced. for a week nothing bad happened. then the warning came on off and on for a few seconds. this happened a couple days in a row. later my car had overheated due to a busted T hose for the heater core. I got that replaced. now the warning only comes on in the morning when the car hasn't been on for awhile, and stays on for a few seconds then goes off. my mechanic is baffled by this and so am i what could this be. it is at the mechanics now and hasn't acted up. it only acted up in the morning the last two days, when i was driving. what could this be would someone help me!

i still haven't gotten any feedback does anybody have any answers

First thing to dtermine what is the actual temperature when the lite comes on, then if it is hot over 225 and the fans won't bring it down, then look for water pump issues or a bad head gasket, no mention of any loss of coolant.