2010 T660 with ISX 450 Mystery Coolant Loss

My coolant level is fine but every time I start the truck after I've been shut off long enough to cool down the coolant light comes on and the chime steady dings away until the motor has warmed up to about 100. It didn't do this when I first got it. Its been doing it for about 2 months now. I'm thinking it may be a bad sensor.

 

Lost a gallon of coolant this week in the pete; still no leaks, but its always poured out white smoke during warm-up. Check engine screen has been up for about a month now, but the company won't get me into a competent shop until its broken down. Any time I go to a shop complaining about the truck stuttering under acceleration before the CEL light comes on swaps out the fuel filter and tells werner its good as new.

 

what year truck? if u have an egr cooler that's probably is leeking. ive had 2 go out on me