My thermostat got stuck to the point where when idling for long periods of time would reach about 100C and while driving would stay around 60C. Since I changed it it stays a tad above the 80 mark and if idled for long periods of time reaches about 90C max.
2003 Volkswagen Golf GL 24,000 miles. 1.9L I-4 TDI 5spd.
1986 300E. 115,000+ miles. 3.0L I-6 1st daily ride, around town only. (Gone)