Hello everyone,

As the title states, my engine has suddenly decided to run a bit cooler than normal. Ambient temperature is about 100 degrees, and even in traffic, the gauge does not reach the 1/2 way mark as it used to before. I've also noticed that the fan doesn't engage as much as it used to, even in traffic. During warm up the gauge indicates a pretty normal temperature increase from cold to about the 1/4 way mark, after which it ends up about half way between 1/4 and 1/2 way points on the gauge and seems to prefer to stay there. At speed, the temperature tends to decrease slightly, as it has done in the past (constant air flow through radiator). The coolant level is normal, the expansion tank cap is new (so is the tank), and in general the system seems healthy. Although I like to see the engine running cooler in this ish weather we are having, I'm a little worried about its sudden change in behavior. So far I have only two plausible theories:
1) The thermostat is stuck open, and that's why the engine doesn't increase temperature as rapidly. This doesn't explain why its running cooler in general though. (The thermostat is 2 years old, temperature spec unknown)
2) There was a restriction or a clog somewhere and suddenly it is gone. More flow=better cooling. (The coolant is 2 years old, BMW blue)

Is there anything else that can cause this type of sudden change?
Thanks in advance for any input.