Over heating issues, sometimes it will over heat and sometimes it will run right with out going no more then 1-2 bars over the middle indication line

What is your question?

A check engine coolant levels low will appear as well as engine coolant hot and idle engine or stop engine will appear in the information indicator on the dash. Some times during the day it'll run fine all day then at nightfall it'll start over heating and the heater will blow cold air when it starts to over heat. Also the hose that is for pressure release on the surge tank does not release any pressure it don't do any thing at all the hose will have allot of pressure in it too. When engine is stoped and turned of the temperature level goes down fairly quickly but then will shoot back up fast once you start driving it again then at times it'll do that we stop car every five mins then the heater will start blowing hot air again and it seems to run fine with the temperature gauge only reaching two lines above the half way point.

What makes this problem better or worse?

At higher speeds it will sometimes bring the temperature down and when at a stop light it'll get hot again and sometime letting it idle brings the temperature levels down but not always

How long has your 2002 Cadillac DeVille had this problem?

A few months or so