Have been noticing a bit of what I think might be overheating of my 98 Deville Northstar on pulling hills or driving slow...coolant temps have gotten up to 229, not sure if that is "normal" for the northstar or not?? (However, the overtemp idoit light has never came on yet.) Only have 31K miles on it, yep and is a 98...typical story...little ol' lady kept in garage and didn't drive if much. Ok, so not sure if I have a problem of not...thinking about flushing system and putting in new pre-mix DEX..but hearing scary stuff about DEX....what is the "truth" on DEX?? (And how will I recognize the truth??) Also considering changing out thermostat?? But car runs at 196-201 on mostly level roads. Also noted it seems to burn off about quart of oil (I'm using synthetic oil - Mobil 1) after about 1000 or so miles??