BMW X5 3.0 Thermostat?
 

Hello, I have a quick question. How can I tell if the Thermostat is good or bad ? is there a quick way to figure out ? here is why.
A while ago 2 months ago the coolant temp was reading extremly high (Needle on red) as soon as I start the car. After I started driving on the freeway it went down to the cold (Needle near the blue)
Last week, weather changed and it warmed up, so I was running the AC coolant temp was at vertical were it needs to be. But I got a service engine soon light. I checked the code and it was P0126 (thermostat), so I cleared the code and been driving it. Today I drove around 100 miles back and forth with the AC running high and low speed and the needle stayed very much at vertical. No light came on or anything sofar. what do you suggest ? shall I replace the thermostat anyway ? or shall i wait and see ? vehicle has about 120K miles.

Same thing happened to me and it's the thermostat going bad. Replace it and you'll be fine.

+1 "preventative maintenance"

Ok, thanks for the feedback guys, I ordered the thermostat and the gasket already. Anything I should be aware of ? suggestion ?

you may want to change the water pump too while you are at .especially if you approaching 100k .

Ok, great thanks a lot. I will go ahead and order it as well ! its got about 120k Miles what about the hoses did you guys changed any or as long as its ok to keep?

I changed the upper, lower, and expansion tank as well.