2004 Oldsmobile Alero

check that the rad has enough coolant by removing the cap when cool and starting it and watching for coolant at the cap location as it warms up and expands when coolant is there put the cap on ,, if its low or air locked you will have to add coolant or some water while its running .

If your cooling system is good then it is a known glitch in the temp gauge. If you bought a code reader and ran live data you would see the engine coolant temp Is actually just fine. Oddly enough as long as it isn’t literally overheating with a red warning light or in the red in general you are fine. No fox has been found for the supposed overheating Oldsmobile alero. I’ll tell you it isn’t actually overheating. The temp gauge just reads from half or just below half while driving and up to 3/4 at idle. Sometime lingers above half while driving also. Very weirdo just a glitch nonetheless.