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So about two months ago my car threw a check engine code. I connected it to DIS and it was a faulty thermostat 2Ef4. I kinda delayed this repair until last Saturday that I had time available. I went ahead a replaced it with this thermostat https://www.ecstuning.com/BMW-E60-550i-N62_4.8L/Engine/Cooling/Thermostat/ES2807159/ it was more expensive and I chose this one because it's supposed to regulate the temperature at 90C. But today I got another check engine light on my way to work. After I got home I decided to connect my diagnostic tool and guess what. I got the same code again stating a faulty thermostat.... have you guys experienced something similar before? What do you think about this thermostat? Because this thermstat opens up at about 90C, could this cause the DME to throw a code since the original thermostat it's supposed to open at about 105C? Thank you!
 

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I'm not completely certain but mine was throwing a code for not reaching operating temp (too cool) so I'd imagine a low temp thermostat would do the same thing.
 

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BMW thermostats have a small heater in them, so the ECU can trick the mechanical thermostat into opening sooner, allowing it to control coolant/engine temperature electronically. With the electric waterpump in my 530 (N52), it can also vary coolant flow to get temperature where it wants.

When the heater fails, the thermostat keeps working but only at the higher temperature. Hotter engine is more efficient, cooler engine is more powerful (denser air = more oxygen = able to burn more fuel). So if you replace the thermostat with a non-standard cooler temperature unit, the computer can't control temperature where it wants, and it complains.

Turner's thermostat selection lists a bunch of different temperature ranges for various engines, but points out the cooler ones are intended for racing applications, sometimes with an aftermarket ECU. https://www.turnermotorsport.com/c-107-bmw-thermostats
 
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