Cadillac Newbie

Guys and Gals,
My wife and I just bought a 2005 Escalade and a 2003 CTS, love both cars but on the CTS how do you know when the car is warmed up since there is
no water gauge. Any one else besides me think that's odd, my wife usually drives the Escalade and I take the CTS, which is a dream to drive even if it is a 2003. Also is there any way to change the OnStar antenna for something more modern?
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