Loss of coolant
 

No leaks visible no puddles. I am guessing a gallon per month. No noticeable white smoke/steam. Seems to run great has power. However I do notice a slight studder almost undetectable "backfire" is the only way to describe it occasionally ( every 3 -4 minutes) when idling.

Head gaskets startin to go replace coolant cap and delete egr at the same time