Thermostat reading BLUE on highway

[aldogg7]

Hi, my first post here on 318ti.org.

I seem to have an issue with my thermostat, which I've really noticed since taking my 1995 318ti (M42B18 engine) to a cold winter climate after driving it solely in Miami.

While driving around town or when the car idles, the thermostat reading is normal (needle around 12 o'clock), and the car interior can heat up fine. However, when I drive on the highway for a while, the reading always drops off, and the needle sits in or on the edge of the blue. Then, the car interior doesn't heat up very well. The same thing happens with the gauge even in hot weather while highway driving. Essentially, increased air flow over the engine causes the thermostat reading to drop...I doubt the air flow is actually cooling the entire engine.

Is this a faulty thermostat? Something else with the coolant system?

Thanks in advance!