These pumps can be intermittant.

Do a search about the thermostats...I don't think I've EVER read about a stat leading to overheat on these 30s...

I made a video clip and attached it to this post. It shows the pulsed coolant flow observed via the opened reservoir. The clip is just over a second due to file size restriction. I applied killcrap's failed-wp confirmation procedure (post #6) again this morning and watched over the opened reservoir for more than 10 minutes. The pulsed coolant flow comes irregularly, sometimes with several minutes in between. Does this confirm WP failure?

Not knowing if this is related to engine overheating, hence potential replacement of wp and t-stat, here is what I need to report:

First start in the morning, engine idle in P, no AC: the fan would come turning in very high speed in just a couple of seconds, with very loud fan noise that can wakes up everyone in the neighborhood and no stop. All this without any overheating warning on the dashboard - the overheating warning would come up in a couple of minutes once the vehicle is on local street, then it goes in to a limp mode, disabling any driving capability.

What puzzles me is this: while engine started cold in the morning, why the fan got turning so quick and at such high speed?

Question about X5 models for ordering WP and t-stat. The vehicle I am working on is a 2008 X5 3.0si, all standard options. Following the parts link where It_texan got his parts (my guess), the ECS Tuning parts order page asks to pick a model, with the following choices:

X5 M
X5 xDrive30i
X5 xDrive35d
X5 xDrive35i
X5 xDrive48i
X5 xDrive50i

which are under chassis E70 X5 (2006-2013). Which choice do I go with?

I don't own a BMW and so I have very little knowledge about X5 models lineup. I am helping a family friend. Your advice is very much appreciated.

I have finally got the replacement of water pump and thermostat done over 2 weekends: the first weekend was to remove the water pump and thermostat following the guide by IT_Texan on this thread. Once the components were off the vehicle I ordered the right parts. The second weekend was to reinstall the replacement parts.

The thermostat has one port that has elbow outlet and many online auto parts stores sell the same thermostat with straight outlet. I finally found a matching thermostat on Amarzon, and here is the link:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

and water pump

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

which looks exactly the same as the one off vehicle.

The X5 has been happy running for 2 weeks now. Thank you all for the help.