I have a 2011 cadillac dts premium just had a water pump and thermostat put on it and there is no white smoke coming from it but it runs hot while driving but will stay at half way temp while sitting when it gets hot if I put it in park and hold the rpms at 3 it will start to cool down can someone tell me what this is and how to fix it
did you install it or a mechanic? if a mechanic I would bring it back. if you did it, did you change the thermostat? did you bleed the air out of the system? if not I would start there. also make sure both your fans are turning on. turn on a/c. that should make the 2nd fan turn on. also see if you have any codes.
My guesses might be a clogged radiator or a missing lower radiator support air dam.
I do not know if the DTS has that air dam or not but if it does and is now missing because of curbs or critter strikes it will cause an engine to overheat on the highway and remain normal at idle or low speeds.
Over the years I can’t even remember how many cars I’ve seen approaching with a lower air dam hanging by one fastener and dragging on the pavement. They are made of plastic so there is no noise and the car owner may not be aware of it. At some point they finish breaking off.