Thermostat Mahle or MISHIMOTO

Swapped to mahle and it's good to go.

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.

The Mahle thermostat arrived today along with all the other bits I think I need to put the car back together. The problem is that the new one doesn't quite match the old one.

In regards to replacing the thermostat, Id stay away from Mahle/Behr. I just ran through two that stuck open, so far the Borg and Warner from FCP can actually hold temp @ -19C, which the Mahles could not at -10C.

I have the same one in my E53 X5 3.0 and it takes forever in the winter to warm up. I replaced the old one as it was leaking but the new one takes like 10miles to get fully up to temp. If I have a long coast up to a stop the temp gauge will actually go back down.

I just be replaced mine for the low regulating temperature, and the snag seemed to improve, but it will still pop up and the car is slow to hit temp, slower than it was last winter at least.

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.