Why my temperature gauge goes up 1 line pass half for a while goes back down
Your temp will be regulated within an operating range. One "line" up or down would not be unusual. It probably reacts this way when your cooling fans turn on and off to maintain proper operating temp. As long as it stays in the "good" range and your cooling system reservoir is showing "full", I would not be concerned about it.
Search Cadillac DeVille Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Cadillac DeVille Experts