Ya...about that., Both incidents, i observed no coolant in the overflow. I pointed this out both times i took it in, but there was the usual mumblings that it was fine. "The pressure pulls it out of there" and that the rapid heat up of the coolant ( from 77 to 226 degrees )within 2-3 minutes is normal...its called warming the engine..... but Really. That FAST ?. Anyway. They did say the coolant was low. And "burpped" the radiator. Im not happy the coolant was low, afterall, they did just refill (?) the antifreeze on the previoud visit...just weeks ago.Check your coolant, make sure it's purple OAT not orange HOAT. When we bought my wife's JKU it had the wrong coolant in it. Had to have the entire system flushed multiple times and then had the correct purple OAT installed. Fortunately the two coolants were never mixed, if they would have been...major problems. Good luck.
I used a turkey baster with a piece of clear tubing attached. Sucked just enough out of both the radiator and overflow bottle. Take it outside to check the color in the sun...better be 'Laker Purple'. If the two coolants ( HOAT and OAT ) are ever mixed together it forms a thick gel through the entire coolant system creating huge problems. There's a lot of information on the internet about this.