The chemical was how he confirmed his suspicions. Luckily no coolant got into into the crankcase. It had to be under load to create proper conditions therefore the Dyno. I left Hutchison, KA for Lake Placid, FL, stayed overnight in MS, added about 11/2 gal water next morning, stayed at Wildwood, FL, same amount, 70 miles to Lake Placid, same. I was concerned it would dilute the additive in the coolant and damage the liners, the mechanic wasn't. I don't remember the low level alarm ever sounding at highway speed but slow down for any reason and it would drive me nuts. I suspect the few degrees of temperature drop or lack of turbulence allowed the water to settle below the sensor.