Coolant thermostat jammed open
 

I got the 'service engine soon' light on,
so I checked using an engine fault code reader.
The reader tool shows "Coolant thermostat jammped open".
Has anyone experieced this problem?

I guess I need to replace thermostat...not sure though.
Is it a hard work and cost a lot?

A quick search of this site should give you the information you need to decide whether to do it yourself or not. You can also search pelicanparts.com for part cost and more installation tips and photos. IMHO any repair on a BMW is expensive so I try to do it myself whenever possible. GL!

I had mine replaced as part of the deal when purchasing it. It was about a $400 repair had I had to pay for it.

why do you guys have to type 5 minutes telling the poster to use the search function instead of telling him what to do, if you know.

for OP. you have to remove the belts. if you decide to do it make sure to cover the radiator on the inside with a cardboard, this way you can avoid breaking the radiator if the key snaps with the bolts. you will lose some antifreeze.