Just finished this myself.
Here is another good reference:
I will add some notes:
1. I cannot imagine getting this done without
removing once side of the VANOS oil lines. I removed the passenger side (US) which is one banjo and one hose clamp, and bent it up out of the way.
2. The difficulty with removal is caused by two factors:
1. there are two sliding 'joints' on each tube- one at each end. When pulling you get motion of both joints before one releases- if you could hold the tubes 'back' it would be easier- in any event, it takes fiddling. (To clarify- if each end has 1/4" of motion, it takes 1/2" overall to pop them loose. If you could ensure that only one part moves you can do it in 1/4". On disassembly you cannot control this- however on assembly, you place the tubes all the way in, so the final positioning is just that last 1/4".)
2. The end of the thermostat hits the bottom, fixed housing- If you can pry the old thermostat loose, and cant it slightly, this will give you a bit more motion to get that upper section out.
3. You MUST use lube. I used silicone o-ring lube for pool parts, plenty of stuff can be used. I was concerned with compatibility, but I think petrolatum (vasoline) should be good.
4. ALIGNMENT. Once you get it apart, try test fitting/inserting the tubes with o-rings into housing (out on your bench, in the light.) Get a sense of how this assembly should work: There is slight chamfer on the outer bore, and the oring- as it sits in it's groove on the tube- must contact this chamfer equally all around the circumference. Any 'tilt' to the tube (and the o-ring) relative to the housing/chamfer will cause the o-ring to push out - and get crimped or sheared off on continued insertion. If it is in equal circumferential contact as you push, it will go in and not get crimped
This is the key to the job. IMHO.
5. Grease up all o-rings. Grease up the housings on the engine and the thermostat housing. Carefully install the three tubes into the engine. FEEL for that alignment- gentle pressure- you will feel the tube 'line up' which indicates the o-ring is in circumferential contact- then gentle push. It should POP into place. Do this for all three tubes.
6. NOW that these three are into the bores, you can actually move these tubes- just a bit- upwards to get ready for the upper thermostat housing...
7. Next trick: Do not fully seat the thermostat into the upper housing- if it is loose, you can cant (tilt) it a bit to allow it's bottom part to clear the lower housing- BEFORE you need to engage all the o rings... you want to avoid trying to jam the o-rings in until it is all in perfect alignment.
So, place the upper part, loosely holding the thermostat in the housing let it tilt, then roate the upper part into the 3 tubes. Once you've gotten the upperhousing in place, you can get your fingers under and pop the thermostat up into it's final position.
8. Now take the time to align everything.... The upper housing should be pretty close to it's final 'mounting plane'- it is down, but maybe a few mm of compression left once you tighten the screws... but pretty much in it's final position vertically- take the three tubes and gently move them down to level- again feel the three tubes and their o-rings all pressing against their respective chamfers in the upper housing- gently but firmly, just ever so slight wiggle, and pop- in they go.
Bolt it up, all done.