Hi, i'm new here from the Netherlands and would like you help you all with a cheap simple solution for my 2017 L405 SDV8 4.4. Autobiography with 105k miles:
I made a bypass solution in a very simple way. A piece of EPDM hose 15/25 (15mm inner/25mm outside) thick and 1 meter long. Hose can go up to 120 degrees. I also had a coolant leak above the rear subframe so a very difficult spot. Thought of several possibilities but this is the simplest solution and costs 2 hours and 10 euros for the hose (1 meter). The aluminum pipes are loose about 1 liter of coolant when cutting the pipes. Be careful because at the first cut the coolant squirted out. So put on safety glasses and old clothes. I secured the rubber hose to the diesel tank mounts with tie raps so it's rock solid. The epdm rubber hose is pretty stiff so I had to heat it with a heatgun. With water pump pliers and some pulling and pushing I managed to pull this hose 4 cm over the aluminum pipe. Used 4 stainless steel clamps for 2 euro. The gray electricity box is only needed to make the workspace a little bigger. I used a multi tool to cut the aloy pipes. Watch out for the red flat cable and black thin plastic tube. Because otherwise you got a much bigger problem.
What the consequences are for the operation of the 4 zone air conditioning in the rear, I was just curious about that. I can tell you now: the hot air just works in the back, also separately so you can still control left and right separately. Left 22 degrees and right 30 degrees just works. This hot air comes from the front and runs under the center console to the back with a black flat plastic tube. Air conditioning I didn't do anything to it so just works. So what is not working now that the bypass is made? Only difference is that the there is NO warm air coming from above. So the rear fan in the ceiling next to the interior light by your head is not giving out warm air. That's all but for me no issue.
Summarized: 2 hours and 12 euros (or like £ 10 pounds). Filling up extra coolant was needed due to the loss of1 liter. Only 0,5 liter was enough because the rear coolant circuit is much shorter now (i think 2 meters each pipe so 4 meters in total). And special thanks to my dad, he supported me.
Update 2 days later after the repair: coolant leak!
Oh no... not again... I looked under the car. I forgot to put an end cap on the cutted pipe to block the coolant circuit to the rear unit. Only a bypass is not enough so close the aluminium pipes (between the rubber hose on photo 2, on photo 2 these are open). 5 minutes work. There is apparently still plenty of coolant in the cutted pipe so that was the reason of the drops of coolant on the driveway. Now its closed and fixed
.
This is the rear hvac heater control unit that needs coolant to heat (no. 5 in the drawin above). Part no. HY3218D283AA. This part is located in the trunk. It has 2x air conditioning connections (inlet and outlet) and 2x heater coolant connections (inlet and outlet). So in my case, this part is no longer getting coolant.
This part is located in the trunk on the left side, behind the grille (intake). Needs quite a bit of work to access this. Interior lining has to come off for a large part in the trunk. In many cases this is not necessary. The hoses are in the rear left fender. For this you have to remove the interior fender trim