For those like me that just need to replace the thermostat, hopefully this will help. I took a few pics, but will mostly describe what I did. I found the attached document on the
Water Pump & Thermostat Install - N52 thread by ENINTY very very helpful.
With 4 litres of BMW antifreeze, 4 litres of distilled water and a new BMW OEM thermostat I set to work on this.
Just to make things easy, when I refer to a location "left", I mean left side of the car as it is if you are sitting in the car, and right same thing etc.
Preparation:
Gather all the tools that you will need, get the car up onto ramps or stands high enough so that you can work comfortably under there. I recommend lifting the rear too so that the car is fairly level. Remove the engine underpan as well as the underpan beneath the radiator. Remove the electric cooling fan, you will need to remove the intake in order to do this. Open the coolant reservoirs and then with an appropriate size catch can in place, drain the coolant from the bottom of the radiator by carefully removing the blue plastic screw plug - this is located on the bottom left of the radiator (left side of the car). It helps to place an old towel or something to catch some coolant that will splash as the flow reduces.
Getting the thermostat out:
1.) I suggest pouring the coolant that was drained into a container(s) for safe disposal. At this point I also suggest replacing the blue screw drain plug (some opt to replace with a new one). It does not need to be tightened up all that much since it does not rely on how tight it is in order to seal. Place the catch can under the right side of the car for the coolant that will come out of the thermostat. I recommend lots of cloths and old towels because there will be spillage. I also recommend wearing some safety glasses (I am not someone that generally bothers with that sort of thing, but coolant splashing on your face and specifically in your eyes is not fun).
2.) From under the car, carefully unplug the electrical connector to the thermostat and move it aside. To gain extra slack, you can unclip the cable harness for this from the clip at the water pump. Next loosen the metal hose clamp on the big hose that connects onto the thermostat (the U-pipe that connects the water pump to the thermostat). Slide it up and out of the way so that you can work the hose off. This was particularly messy and ended up getting fairly soaked in coolant. The hose is usually fairly bonded to the connector on the thermostat, so it needs some careful finessing. There is a fair amount of coolant that needs to come out of the thermostat and water pump, so as you work the pipe off the soaking begins. Eventually this actually helped break the bond and the hose came off with relative ease, some more coolant drains out. Slide the metal hose clamp off the hose and put it aside.
3.) From above locate the BMW plastic hoses and remove the metal clips by using thin needle pliers. This prevents the chance of losing the clips which is something you want to do. Remove the clips and put them aside. With a careful rotating force, pull the large BMW plastic hose until it pops off. You can carefully push it down and out of the way. With the same technique, remove the smaller BMW plastic hose. In both cases, some more coolant will drain out.
4.) From under the car, you can now remove the two bolts holding the thermostat onto the water pump. Back up to the engine bay, you can now carefully manoeuvre the thermostat out so that the metal hose clamp on the smaller hose can be loosened and then removed, and again, slide the metal hose clamp off and put aside. You now have the thermostat out of the car.
Fitting the new thermostat:
1.) Start by putting the metal clips back onto the BMW plastic hoses and clip all the way down. Put the small metal hose clamp back onto small hose and connect to the new thermostat on the appropriate connector. Without tightening the small metal hose clamp, manoeuvre the thermostat into position ensuring that the hoses are not twisted or snagging in any way. Get under the car to double check that the small hose is not twisted. Back to the engine bay, carefully get the thermostat back out again ensuring that the hose does not twist or change how it is orientated. Make sure that the hose is all the way onto the connector and then tighten the small metal hose clamp securely. Again, manoeuvre the thermostat back into position ensuring that the hoses are not twisted or snagging in any way.
2.) From under the car slide the large metal hose clamp onto the large hose and fit onto the thermostat connector. Secure the thermostat to the water pump with the two bolts. Make sure that the large hose is all the way on and then tighten the large metal hose clamp securely. Plug the electrical connector back onto the thermostat and the cable harness back into the clip.
3.) From above attach the the two BMW plastic hoses back onto the thermostat. You will need to push them on firmly until you hear a click, it's on. The thermostat is now fitted and all hoses are connected. At this point I suggest verifying that everything is securely fitted and tight.
Reassembly:
To make fitting the electric cooling back into the engine bay, you can undo the thin over-flow coolant hose from the coolant reservoirs and move aside. Get the electric cooling back into place and secure, putting everything back where it belongs. Refit the thin over-flow coolant hose onto the reservoirs. Refit the intake and all electronic connectors.
Refilling coolant:
Open the bleed screw 4 or so turns and slowly pour in the pre-mixed coolant up to the bottom of the filler neck until some coolant comes out of the bleed screw without and air bubbles (use some cloth or paper towel to soak this up). Close the reservoirs and perform the vent procedure (ignition on with the climate control on max temperature and lowest fan speed, throttle pedal to the floor for 10 seconds - this takes 12 minutes, so pay attention to the time when starting this). Check for any leaks. Once the vent procedure is finished, open the reservoirs and top up if necessary. Repeat the vent procedure again. You can recheck the coolant level once more if you want and repeat the vent procedure one last time. It is a good idea to put the battery on charge while doing this in order to prevent the battery from running down.
Finishing up:
Refit both the underpans and you can now get the car back down onto the ground. With the hidden menu activated, start the engine and keep an eye on the coolant temperature, check for leaks too.
Some pics:
Don't lose these metal clips.
The new thermostat located to get the correct hose orientation before being manoeuvred into position.
The new thermostat fitted in position with all the hoses now connected.
From under the car, the new thermostat fitted.
Hopefully I have covered everything here, but I strongly recommend using the document on the linked thread.
Sadly my over-cooling persists, I really have no idea why. I replaced the temperature sensors a while back, so was convinced that it was the thermostat that was faulty.
Have posted this in the
Pictures: Electric water pump + thermostat replace thread too -
here...