Was towing 3 tons (6600lbs) for the first time with the X5 yesterday so I engaged a spare mobile to look at a few parameters over OBDII via bluetooth. Car is early 2010 35D with 3.0sd engine. ECU has been re-mapped by the previous owner....

I was concerned about Water Temp as it is a good indicator of what's going on...
Also looked at Manifold Pressure and Air intake Temp. This what I saw:

1) Water temp is around the 90°C mark. Max it reached was 108°C when it decided to charge up a hill. This was the only time it went over 100°C.

2) Manifold Pressure seemed to max out at 2.55 bar. I'm sure it was higher than that because 255 sounds like the max of an 8-bit number... anyway I was amazed that the boost pressure is over 1.55 bar (manifold pressure is 1 bar with engine off). My last foray into turbos was in 2001 with a 911 turbo and that was 'tweaked' to 1 bar from 0.7 bar. Amazed that a diesel is up so high, but I guess that is technology for us....

3) Intake Air temp seemed to be ambient plus 10°C, so I guess it is being regulated with the intercooler. Does efficiency improve with lower charge temps, like petrol engines?