May-2018 update:
Well the car has been doing it's duties as the mommy-mobile the last few months. We also had booked a trip to the KZN south coast for the recent long weekend at the end of April, so I was looking forward to enjoying the space and comfort on the long drive.
And then the sh1t started....
25-April: my wife is in eyesight of our house, and the car pops up a yellow warning message that it's hot - proceed with caution. As she pulls into the driveway, the yellow message turns red: engine overheated. I got home a couple of hours later and did some checks: no leaks under the car and the expansion bottle is still on the max. indication mark, so no fluid loss.
DannyBoyOPC came through to scan for codes, and there were some issues about forced upshift to protect engine, and also something about the waterpump not operating due to a blockage. Now bear in mind, when we bought the car, it went to BMW for it's final service before going out of plan, they found a water leak on the pump, and replaced the water pump, along with 2 water hoses, that was 18months/12000kms ago. They didn't replace the thermostat (why boggles my brain - makes sense to do both), but anyway...
So Thursday, 26-April, I source a new thermostat from BMW, which I only got that afternoon. Danny came to help again, and we got the car sorted early evening. I test drove about 30kms that evening and all seemed well. No warnings, and going into the hidden menus showed the coolant temperature fluctuating within the acceptable range (which led me to believe the thermostat is working.
Friday, 27-April, 3am: We're on our way to the south coast. Then just after passing Heidelberg, the car pops up the yellow warning light that it's getting hot, and shortly after that, the red warning that it's overheating. Thankfully it was just as we were passing a Total garage, so we pulled in there and waited for things to cool down.
After much swearing, we decided to turn back, and try limp back home and swap cars. Starting the car up again, coolant temp was on 72 degrees, and on the route back home there were no issues, no warnings, no overheating.
Fast forward to 3-May, and I booked the car in at BMW for checking. Our thinking is that the water pump electronics are faulty, so sometimes it works and sometimes it decides to say it's not working. I'm still awaiting feedback from BMW. If it is the water pump, it's still within the 24month warranty so they should then replace it.
Really odd and intermittent behavior, but that's electronics for you.
Will update once I know more...