Q: Radiator fan started to run - and stayed running - while on freeway on cool day. on 2004 Saturn Vue

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
I know my thermostat is 'broken' - it's been running a little cool (gauge at 45%)and is slow to heat for over a year now. My IR gun says temp of upper hose near engine is 165-170. For a $300 simple thermostat replacement bill,I'm OK with that. Gas mileage is great (got 31 on last trip).
However, recently...
When I came to the end of the freeway offramp (and road noise) I heard my radiator fan running. A few miles later when I parked it was still running and would run about 5 sec after starting the engine. The dash gauge was reading just a hair cooler than 'my cooler than normal' normal - say 40%. Hours later, it still ran after starting the engine. At the end of that return trip I opened the hood and felt the lower hose - it was COLD. The upper hose was very warm. Here's the good part - when I squeezed the lower hose - just to see if fluid 'gooshed' up into the reservoir (which it did) the FAN TURNED OFF!
Tthe SES engine outline light came on after charging down a ramp - it went off a day later. It's been popping on and then off a day or two later a few times now. (I wish I had a code to give you, but I don't.)
Now, massaging the cold lower hose doesn't necessarily turn the fan off.
After filling up after a freeway drive (and the fan still running) I made a sharp swerve into a left-turn and the fan turned off. When I got home I felt the lower hose - it was warm. All this time the dash gauge was at 40%. Oh, when I was on my long freeway drive I turned on the heater to full blast, just to see how hot the air was, and the SES light came on. The air temp ramped up to what seemed a little too hot and then seemed to slowly drop a little - the dash gauge even seemed to drop a hair.
Today? The SES light is off, the fan is not running, the lower hose is quite cool and the upper hose is nicely warm. What the heck is going on?
(1) Answer
(1) Comments
You most likely have a broken thermostat and the pieces are moving around and causing unusual coolant flow, which explains the erratic cooling fan operation and the SES light on/off etc. I would get that thermostat replaced ASAP, because they can jam the coolant flow completely and cause a severe over heat and ruin your engine. The Saturn VUE engine is a SAAB V6 engine and the thermostat is really buried, I have done a few.

Huh, have never seen/heard of thermostats breaking into pieces, but now that you mention it I can visualize the spring breaking (a year ago?) and then a coil chunk 'unwinding' off the center post to become lodged against the thermocouple every now and then.
This scenario fits if shorting out the thermocouple makes a 'too hot' signal to the ECU (or is it ECM?).
At least a spring chunk isn't going to impede water flow (until it finds the water pump).
I think I'll be replacing a thermostat very, very soon! Had to happen sometime anyway. Thanks for the 'KITB'. :-)