I checked all the connections again and the boost accumulator hoses as per Peter's instructions and all appears good. I took it for a drive, only the second time with the oil cooler. It seemed to hit boost just fine, not sure what was different. I think possibly the JB4 was calibrating or adapting to the new oil cooler and thermostat during the first run? I have no idea.
Car seems to pull really hard, even had a bit of fun with a Ducati bike on the way home, think I caught him by surprise
Straight after that run I went into limp though! Turns out it's an ongoing Vanos Solenoid issue that I've been having.
Also, I got a warning light for oil being low, and then later at minimum on the idrive. Never had the oil that low before! iDrive said to fill up with 1 litre of oil immediately. I went home and filled up with 1.3 litres of engine oil. I think I was down on oil mainly because a decent amount of the oil was still inside the stock oil cooler lines that were removed, plus I had a couple leaks initially because I didn't tighten all of the fittings when I started the car. All good now!
Updated the JB software, change the cold/hot oil protection to run off water temp instead and the car feels like a beast. Not sure if it's in my head or not but car seems to be pulling a lot harder. Seem to be breaking traction really easy... on a roll.
Temps seem to sit around 90-100 degrees celsius. Only gets up to 100 if I do a few pulls but it drops back to 95 fairly quickly. I can literally see the oil gauge needle moving. I have not had a chance to beat on it hard though, but I can already see a huge difference.
So far the oil cooler is doing it's job, very well too. I'll keep updating this thread as I put more km's on the car and see how it holds up. So far so good.