Thermostat MISHIMOTO or OEM BMW

I was instructed by a friend who had some of m47 and m57, to buy thermostat only original from bmw, because everything else doesn't work as long or good.

I have a mishimoto thermostat with their radiator setup. It does kick on the fans on at a lower temp range than when the stock one would which is good. I had issues running hot on the stock rad/thermostat and haven't had any issues since.

The replacement thermostat came from BMW. No problems this time.

I replaced the thermostat with a Mishimoto thermostat and vaccume filled the coolant. I did a 30 min test drive in the 95+ weather with the AC cranked. Never went past the 7th dot.

I wanted to upgrade from plastic and got an aluminum Mishimoto thermostat, but i didn’t notice that it opens at 180°. Can i get away with the 180° thermostat, or should i ship it back and re-order a different, higher rated thermostat?

mishimoto changed the design of the thermostat when I purchased and you will need shorter bolts they are not provided

I replaced the t-stat with a genuine part and again no luck.

I got a bad mishimoto thermostat with similar results.

Changed to genuine thermostat, no change. Needle tends to dip on higher load highway driving, but only occasionally. Obd temp is between 77C-88C.

I bought and installed a Mishimoto thermostat that activates at 68°C, while my vehicle OEM (Original factory) thermostat activates at 88°C and fully opens at 100°C. With the Mishimoto thermostat (68°C), the coolant temperature basically stays 71 ~ 74°C when driving, from OBDII reading. Short Term Fuel Trim was OK, between -10% and +10%. I checked the spark plugs after one week, they were fine.

However, after three weeks (last Saturday to be precise), the Check Engine Light was on when I started the vehicle, and OBDII gave Code P0128. I searched the code online and got: coolant temperature fails to reach the proper operating temperature, or Coolant Temperature Below Thermostat Regulating Temperature. My thinking was the engine finally realized that the temperature was below the operating temperature, due to the Mishimoto thermostat.