So after owning the ST for 2+ years, I've came across the first real drivability issue... that I didn't cause at least. Last week was warmer that normal in the 90s. I know, it's hotter than that in the SW, that's why I don't live in AZ any more. Beautiful scenery, but I just got tired of the warmer days.
Anyway, I've been running with the AC on and notice the temp gauge higher than normal. Truck usually ran halfway for the last 2 years no matter the temp. So running at the top end of the normal range I figured the heat was causing it. Did quite a bit of running around and noticed that the gauge had dropped when I came to a stop light. Then rose back up when I started driving. then settled around 3/4 gauge at cruise. AC started blowing warm for a minute then cooled as normal. I thought the fan clutch was acting up, so I was going to check this weekend for the typical overheating cause items. Well on Friday morning on the way to work, AC off, as it was 62 outside, temp gauge rose to the top of normal range on the highway and realized there is more than I thought.
Friday: on the way home it was running hot again and fluctuating as well. Got home and did a quick check, fan clutch is weak, felt the radiator cap which was at best only warm, upper rad hose had pressure but also not very hot, coolant reservoir was pretty full, and heard so bubbling around or under the intake. Pretty sure the t-stat is failing. No drips under truck either.
Yesterday, ran to the zone and picked up coolant, t-stat, and a rad cap. Started draining the radiator and removed items to get to the t-stat. The rad cap was stuck but came off with some persuasion. Drained the overflow tank as well. Popped out the t-stat and inspected it. From what it looks like the t-stat was not operating properly and the rad cap was stuck. Replaced both, refilled with new coolant, and test drove. All back to normal and didn't go passed half gauge.
Going to replace the fan clutch in the near future as it is old, weak, and probably farts dust from time to time.