djb383

Point the temp gun at the t-stat cover. If the temp gun and the factory gauge indicate about the same temp, say 115ish, then suspect a stuck open or no t-stat. If the temp gun indicates 190ish and the factory gauge indicates 115ish, suspect a bad factory gauge/sending unit/something electrical regarding the gauge.

This time of year, and with a healthy cooling system, coolant temp should run/range fairly steady with the temp of the t-stat.......for example, with a 180 t-stat coolant will fluctuate/range +/-180-195, with a 195 t-stat coolant will fluctuate/range +/-195-210. The t-stat only controls minimum coolant temp and again, I'm talking this time of year. Six months from now, max normal coolant temps can be well north of the t-stat temp. The XJ cooling system is mediocre at best and I can't stress enough the importance of good cooling system maintenance......all cooling system components must be in perfect operating condition at all times.