Gawd these cooling systems are complicated. Ive been spending a couple of days reding up on them.

That thermostat only affects flow to the transmision oil cooler.

When engine is cold:
- The engine thermostat shuts cold water flow into the engine so it can warm up faster.

- The trans thermostat allows water from the top radiator hose through the expansion tank and to the trans oil cooler, so the gradually warming water heats the atf along with it.

When the engine is warm:
-Engine thermostat opens to allow cooled water from radiator into the engine.

- The trans thermostat shuts flow of water from the expansion tank to the oil cooler and simultaneously opens another coolant path from the radiator, so now it cools the trans fluid.

But yeah, anything slightly out of wack could explain slightly elevated but not overheating temps I guess.

__________________
04 X5 3.0i auto
03 X5 4.6is