It's well established by know that the map controled thermostat is great in theory and improves fuel economy but at the cost of increasing pressure on cooling system (more heat = more pressure).
Also, if component in cooling system fails (and it will), you're much closer to potential serious problem of overheating vs running on cooler thermostat.
I've ran this on my E53 4.6is and have sold few dozen to E39 forum members couple years ago. I've had good connection in Europe and got this for much better price. This is OEM thermostat for E38 740D never sold in US.
https://www.ecstuning.com/b-genuine-...CABEgKFZ_D_BwE
Direct fit other than installing simple resistor into disconnected wiring connector to avoid CEL.