Before you start this be sure that you have the correct tools and that they are in good order, and that you are competent to attempt this job - I nor the forum accept any liability for loss or injury if you use the write-up/pictures outlined below, I am happy enough to tackle this job myself and feel that I have the necessary tools and experience for the rask.
Had the usual issue with my Compact recently not getting up to temperature (2001 M54 325ti).
I guess at nearly 80k it only to be expected, so I made use of the midmonth31 offer on EuroCarParts and bought some bits to get the job done, I decided to replace the water pump and coolant at the same time to try and ensure reliability.
Remove the clips holding the air intake over the top of the radiator and put it to one side.
Remove the T25 torq screw.
Remove the clip on the other side next to the expansion tank.
Unplug the fan and fan speed controller.
The fan unit pulls straight up, remove it and put it to one side.
Slacken the 10mm bolts holding the waterpump pulley in place.
Using a 16mm socket remove the tension on the drive belt tensioner and slip the belt off.
Remove the undertray from the car and remove the drain for the radiator, catch the coolant in a suitable container and dispose of it correctly. Remove the expansion tank filler cap to assist with draining.
Remove the water pump pulley and slacken and remove the 10mm bolts from the water pump housing (four in total), use 2 M6 bolts to remove the water pump from the block.
Unplug the temperature sensor on top of the thermostat (cut the cable tie for the wiring from the top hose - not pictured)
Pull the clip holding the top hose to the thermostat housing and remove the hose from the housing.
And remove the clip and hose for the bottom hose to the thermostat housing.
Undo the three 10mm bolts holding the thermostat housing to the block.
And the 13mm bracket (there is a 13mm bolt behind the bracket).
Remove the thermostat from the block.
If you are lucky (not like me) the bolt won't snap in the block and refitting is the reverse of removal - otherwise, good luck removing the snapped bolt!
I tried to remove the bolt with a stud extractor and welding a nut on the end but alas, in this case it wouldn't shift. To give myself some more room I removed the radiator and expansion tank cut the bolt flush with the block and drilled and tapped it to the correct size and replaced the bolt with a new stainless one.
BMW TIS - 11 28 010 Replacing alternator drive belt (M52 / S52 / M52TU / M54 / M56)
BMW TIS - 11 51 000 Removing and installing complete water pump (M52 / S52 / M52TU / M54 / M56)
BMW TIS - 11 53 000 Removing and installing/replacing coolant thermostat (M52TU / M54 / M56)
Bleeding the cooling system can be a little difficult on this engine, I had to do it three time to get rid of all the air - I used Ronnies guide here:-
The final result is that the car warms up much quicker now and holds the correct temperature (12 o'clock) on the gauge. I hope that the guide and pictures help someone.