temperature gauge movement on 2000 Sienna CE

Your car will run hotter in stop and go traffic. Your cooling fans will kick on every now and then to keep it cooled in to normal operating temps. But in high way driving it will run cooler due to the steady flow of air thru the radiator caused by your driving. Although it will stay in operating temps then also. If it appears to be a rather large swing in temp range from stop and go to highway driving I would check your cooling fans to make sure that they are coming on properly at an idle. If thay are not coming on that is what is causing the large swing in temp and you will need to get them fixed or replaced. Hope this helps.