Recently started to notice coolant loss. Pressure tested it, no obvious signs of leak, seems to hold pressure. Rarely drive it now but make me add coolant after every drive. No smoke, I thought maybe bad headgasket but no milkshake, no smoke. Got 178k miles on it. Runs well. Real head scratcher. Drive it maybe 800miles/yr. Any guesses? Has coolant line deletes under plenum.