90C if perfect for aluminum heads. I've experiment on a few domestic engines. Carb and fuel injection. The high temp is for emissions. My '21 HEMI was lowered to a 194F thermostat (203F stock). No lights and great for summer Texas heat. It passed emissions testing in my county. Even better for highway use. I didn't like it reaching 220F before air dams opened up to cool it. I removed a few air deflectors to keep it at 90C all day long. My '83 C10 with a crate ZZ4 motor also uses a 194 thermostat. Best gas mileage is obtained using a 90C thermostat. Too hot boils fuel. Too cold and optimization suffers.

My 3.0i has a new thermostat It runs right at 194F. I saw no lights and smooth running.

Install it!!

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'06 X5 3.0i - bought @143,123 miles (12/26/20)