The stat doesnt measure anything.
It controls the flow of water thru the radiator.
When its broken, it opens too early, or simply never closes, which means too much water flows thru the radiator, and the engine never warms up. These engines are fitted with an oil cooler, which uses engine coolant to reduce the oil temperature, so if the coolant temp is low, the oil will be too.
The instructions above are for a 4 cyl engine, the v6's are much harder, as the stat is behind the timing belt.