My 2010 Ram 2500 4wd coolant levels started fluctuating at first atbidol then when moving. Will go up to 250 trigger light and chime then drop right back to 199. Added 3/4 gal of zerez g-05 coolant.

Thought coolant might have been left low
after both side intake gasket repair. So
added the 3/4 gal. All was good for about a
week. Even sat at idol yesterday for 30
minutes and held at 200. On a later restart
heater started blowing cold checked
coolant added the other 3/4 gal. Heater was
blowing warm again. Don't know where
coolant has gone since there are no signs
of any leaks. Any ideas where to start.