[shadow135i]

Wanted to update this thread for those that might be looking into doing this themselves like I did this past weekend.

Thanks again Joe-BMW33 as I was able to order the correct parts and have everything I needed to get this job done myself!

So I only replaced the turbo return coolant lines on mine and my reasoning was two-fold:

1. The return lines are the highest heat stressed lines in the system if you look at the cooling schematics. This is because they are routed above the turbos (heat rises) and the "cool" coolant supply is actually routing from the engine return, so the supply lines are as hot as the engine return for the high temp circuit. And anecdotal evidence I was able to gather from the internet showed me that the failures, at least for the TU2 version of the engines, are occurring from the turbo return line side, with the supply lines looking to be holding up for the most part.
2. I was lazy and didn't want to completely remove the turbos along with the associated oil and coolant supply lines. Though note for others you do still have to remove the oil supply line for the passenger (right-side when in the car) turbo in order to get to the coolant return line.


Also, some helpful notes for others who brave taking on this job:

1. BMW still doesn't give us a simple coolant drain plug so in order to drain the system you need to disconnect the lower radiator hose that feeds the main mechanical coolant pump. It makes a huge mess that I haven't found a good solution for so I just clean the area in the engine bay as best I can to keep coolant from corroding things, but I'm sure there are spots I missed that I couldn't access or see.
2. These engines have to be vacuum filled to prevent air traps from forming in the cooling system. You can get some cheap kits from the internet but you will need an air compressor or, as in my case, a vacuum pump with the right quick connect fitting to pull a good vacuum on the empty system.
3. Applies to 2018 M550i's at least - WARNING: Make sure both the high and low temp expansion tanks are filled to the max level before doing this as both systems will be bled using this procedure. If the low temp circuit is low you could damage things in that circuit following this procedure. To initiate the car's bleed procedure after filling the system (with the above mentioned vacuum tool) you need to do the following steps: Turn on the low beam headlights and hazard flashers, buckle the driver side seatbelt, press the start-stop button 3 times in quick succession (a confirmation on the dash will show "diagnostic mode active" if you did it quick enough), turn on the A/C to max heat (84 F for those in the US) and the fan blower speed to the minimum setting, start the car (idle speed should stay at 1200rpm), rev out the engine to 3500rpm for 10s at a time 5x with 30s breaks in between at the higher 1200rpm idle, car will idle at 1200rpm for about another 8 minutes after you finish the 3500rpm revs and then finally lower back down to the normal 800rpm, after that you repeat the 3500rpm 10 second holds for 5x with the 30 second 800 rpm idle, finally after that you can shut off the car and wait a couple of hours for the engine to cool down and top up the coolant reservoir if it dropped any from when you started the test.


Good luck to others who attempt this themselves and hopefully you guys will have more info to start with than I initially had!