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

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?
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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'. :-)
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