Like the SAAB experts here are saying, its probably the tempsensor.
But here is what happend to me when I first started a 3.0, after a headgasket and oilcooler job.
I thought I got out all the air in the coolant system, and it was running fine. The temp needle went up and up and then bottomed out. I checked the engine temp with an IR meter, and it was normal, so I let it sit for the night, while I went home and ordered a tempsensor online.
Come back in the morning, and the engine had "burped", so just to have something to do while waiting for the sensor, I filled it up with coolant and let it run a little.
Now the temp was perfect, so I let it run more. It turned out that because I didn't bleed it with the bleed plug close to the temp sensor, there was air in that "tube" between the 2 heads. When the air was gone all was good, and the car has been running soon a year with the old sensor.
So I have one sensor for sale....hehe.