Good day. I had posted about my 2010 MCS a few weeks ago and I just wanna follow up and maybe get more input from fellow owners on this forum.

My S threw a P0128 ( Powertrain ) Coolant temperature below thermostat regulating temperature. Approximately the same time, I notice that the gas consumption seemed to have gone up. Changed the temp sensor in the thermostat housing and changed the downpipe O2 sensor. Same thing. Example: I put in gas that was SUPPOSED to get me about 205 miles. I only got about 170 out of it. More freeway miles than city miles and I never gun it at either the freeway or surface streets. In the past, I have been able to get to and sometimes even EXCEED the posted mileage on my front display.

Spoke to a german car specialist over the phone and they were leaning towards the Thermostat housing because apparently, if the thermostat fails to open and/or close correctly, the car would then run rich and cause the problems with the gas consumption. Is this correct? Can someone verify this to be true?

Thank you in advance.

 

When my 2007 S temp sensor failed... it failed hard cold so the ECU ran the car fat rich resulting in a farty exhaust sound and terrible mileage. Once the Thermostat housing and temp sensor was replaced - ran like new again.