EDIT, never mind just seen Mikes mentioned the pump already
Check the water pump, a lot of these were shipped with plastic impellers that fail. Easy to change on an M52. As the others have suggested also try the thermostat while your unbolting stuff at the front.
You can check for excessive overheating with diagnostic software, it logs the number of overheats.
I've recently swapped my fan for a 16" one no idea how that will do as I've not been for a drive with it yet - it just fits on my mega sized rad! I got it cheap on E30Zone so I thought, why not?
I've also now got louvre holes in the bonnet tops at the back.