400i Thermostat

Loosen the hose clamp, remove the old thermostat, put the new, screw clamps of tightening. Oops it's done.
Truly....
If you want to replace inside the carlorsat, that's another thing. We must first find the right thermostat. If you found I can tell you what to do

 

Schumi.....the rubber hose may be stuck on the metal pipes...try to loosen the grip between the two by carefully pushing a small dull point in-between, maybe an old screwdriver or even a chopstick ! You could also try a squirt of spray lubricant of your choice, the rubber is dry and hard.
The plan is to move the point in and out or sideways to seperate the two, start where the rear, longer hose joins the t-stat and the aluminum housing to the rear.....you may need to unbolt the housing from the engine.
It is VERY important to not cause any damage to any of the metal parts, your goal is to split the rubber away from the metal. Work on one joint at a time, if you unbolt the housing first, then seperate the housing from the rear end of the longer section of hose, then work on the forward end of the longer hose where it joins the t-stat, and continue to each junction......it is slow, careful backbreaking work.

Gary

 

You can also use a hair dryer to separate the rubber from the metal. Do not overheat.

 

I was going to say a popsicle stick would work too.....but you got the idea, strong enough to get between the hose and pipe, but not tough enough to cause damage.
Twisting helps also. If you get a good enough grip you can hear the rubber letting go of the metal.....a little wipe of silicone paste before re-assembly will help the next guy.
Might be you !

Gary

 

I used another solution because the pipe was too dry and rigid. I've replaced by truck cooling pipes. I found it in a spare parts shop and I cut to length.
You can find the solution to your problem. The pipes are straight. They have no particular curvature. Good research.