I had a similar problem with my 2005 Jeep Tj. gauges were reading normal, in the 210 region... smack dab in the middle. Diagnostics read the actual temp as high as 229. I had replaced the thermostat three or four years before. Never looked at the stamp in the center. Some read 198, some 203... the temp stamp on mine was missing, or had just run out. I was thinking fan clutch, radiator, fluid... but a new thermostat did the job. Diagnostics read 205 after the new part was in. The gauge more or less looked the same as it did before the fix. Hooking it up to a diagnostic machine at a shop gave me a much more accurate reading than trying to read the gauge on the dash.