I saw another post addressing this but wanted to add my personal experience. My Bronco(BL, SAS, 2.7L) was delivered with the coolant well below the "Min" mark. I chalked it up to Ford bean counters saving a buck and planned to address it when I took the truck in for service. Then the 2.7L failures started to pop up and they look like classic detonation to me. Since these failures all resulted in the destruction of the spark plug, it is impossible to confirm. This brings me back to the low coolant. I wanted to see how low it truly was. I topped mine off and fired up the engine with the reservoir cap off. sure enough, there was air in the system. Where there is air, there is going to be intense heat. I'm not saying this is the cause of any engine failure. I'm simply saying that coolant is cheap, fill your system.