I have ordered a new themostat from ebay. It's on its way.
I just have to build a solid plan in my head first for replacing it. That's why I got so many questions :)

Here is the link:

RealOEM.com * BMW E70 X5 3.5d pollutant reduction cooling

As I said in my post, I recommend the tight reach wrench (link is here) - it made it much easier to get to some of the bolts on the duct clamps.

Also, you might remember the electrical connector (for EGR temp sensor) that I said I had trouble disconnecting? Good to know I'm not alone. Check out posts #60 and 61 on this link - it's for a 335d, but the much of the info is relevant to our 35d. FWIW, I went back and tried the suggestion in post 61 of pulling the white tab all the way out, but I still couldn't get it to work. For me, using a very small flat blade screwdriver slid under the connector from the back side is still the best way to get it apart.

BTW, if you're replacing the thermostat I assume your temp is also not getting above 72-73 degrees?

Regards.

Yeh, my 09 3.5d shows 72 degree most of time, and barely reaching 74. That's why.
Thanks for the link.

bty, the way to unlock and show temperature on the dash is a bit annoy, it requires unlock each time... I was thinking once unlocked, it stays unlocked but my car's code is 26 and I need push 26 times every time...

This might be a good document to list the steps to remove the themostat

BMW Workshop Manuals > X Series E70 X5 3.0d (M57T2) OFFRD > 2 Repair Instructions > 11 Engine (M57T2) > 53 Thermostat And Connections > 1 RA Removing And Installing _ Replacing Coolant Thermostat (M57T2)

which means we don't have to deal with the hose to the right side of it.

I checked mine again and same thing, 74degC max. New T-stat is sitting in my garage but I am out in Whistler for the weekend :-), so will have to wait for another week to do the job.

Once in a while I also monitor my temperature and the EGT if it's regenerating using Torque app on my phone and a mini ELM OBD. I am getting a reading of 80°C-81°C even at freezing temps. And when it's regenerating EGT goes up to 600°C.

Ugh, Sunday morning, just opened the hood on the 35d and surveyed the plethora of parts needing to come off..... Another coffee before breaking out the wrenches seems justified :-)

Update: It is noon. Loosened the two bolts that are clearly one of the hardest to undo since they are tucked way back where the turbo seems to be or whatever that is. Took the two mounting bolts out of the EGR cooler. The electrical connection on the throttle body is indeed impossible to undo without sticking a small screw driver in there and wiggling it.

Got the cover off the bottom and drained coolant by disconnecting one of the two "mystery" hoses disapppearing into the driver's side fender. Apparently no drain plug at the bottom of the cooler as others have reported. Also disconnected the coolant connections to the EGR cooler and yes it is messy!

Not yet bothered with the fan shroud as so far I can tools in there easily enough. So far my knuckles are in tact... :-)

Next is disconnecting the EGR cooler from the throttle body. Sitting back with a coffee for now to contemplate and look at pictures earlier in this thread. I just remind myself of the avoided cost to keep motivated.....

back together and running 86 -89 c
 

It is back together and test drove it. The wonderful BMW people wanted to do all kind of test programs and charge me close to a thousand to replace it....I am switching dealerships for service as the place I previously went lost its service manager and the current one is....shall we say: NOT very good....

Only thing to add are a few pics and a couple of pointers.

I covered the intake to the turbo with a cup lid from a Starbucks cup. That opening is just perfect to drop something in it while you are wrenching!

The tabs on the fan shroud are held in by clips, you have to press the top and pull up a little until both are free. The drivers' side flips inward to clear the top hose on the radiator.

Many thanks to all for good pictures and descriptions, it made it a lot less scary.

^ Congrats.

Sounds like a "4 coffee job"?

;)

Or 3 coffee and a beer, weather dependant ;)