A common issue with the 4/4 models following fitting of larger more efficient aluminium radiator was overcooling John. This could cause thermostat to partially close with extended hysteresis then ironically causing overheating when motorway speeds encountered. Cure was a lower temperature thermostat.
I thought it was worth a mention........something to eliminate in the ongoing diagnostics, A basic like is it getting hot enough for the fan to activate.....a temp sensor whould eliminate that issue, but hopefully the water temp guage ( although not always reliable reading) would also be an indication if it was getting hot enough to trigger the fan....but an indicated 12o degrees temp would indicate a different problem.
I agree most likely changing the radiator caps would resolve the greater capacity issue,, but has that been done on this car?
As it's had its radiator fitted recently, does it have an air lock in the system?
