Thermostat question

[Peter D]

Guys,

The temp gauge in my '04, 3.0, X5 always stayed at the mid point of the gauge winter or summer (110k on it)...

At the end of last winter i noticed that the temp gauge wasn't going over 1/4 after 25+ miles of driving on a cold morning (never got to 1/2) and that i had a bit of milky sludge on my oil filler cap because i wasn't warming up. Spring and summer came and the X went back to normal (no milky sludge, no coolant loss) for the warm months, but now that fall it here, the 1/4 gauge is repeating

My thought is that it is a bad thermostat but then i noticed its got an electrical plug on the housing. Is this electrical connector from a sensor that reads, or is the thermostat electrically controlled meaning that i may have an issue other than a bad thermostat.

I am planing to replace coolant, thermo, WP and serp belts due to milage but I don't want to replace the thermostat to only find out I may have a computer or other sensor that controls the thermostat problem.

Who has best prices, real OEM and ECS seem the highest