I recently upgraded from a F75 to a F78 the old F75 pulled lovely and only ran a little hotter when towing. However the new F78 (80K miles on clock) sopmetimes runs very hot when towing (especially in hotter climates).
The full story: Upgraded to F78. Towed caravan to south france no problems. Pulled over mountains into Spain (ran very hot). Once in Spain I was unable to exceed 50mph as this would cause the temp to continously rise. At no time did I allow the engine to boil over, I simply throttled right back and put the heater on full blast (no fun in Spain). Please note that I have run the exact same route in hotter weather whilst pulling the same caravan with the old F75 without a problem.
The following may be relevent.
1).There is no oil in the water or water in the oil, I am not loosing any oil or water and the water stays in the radiator when the engine is running, thus I assume the head gasket is intact.
2).When I open the fuel cap to refill after a run there is a noticable suck cause by a vacume in the tank. Would this cause the engine to run lean? If so what effect would this have on a turbo desiel?
3).There is a knocking comming from the front of the car on right hand corners. I assume this is the RH CV joint. However I assume that this shouldn't be turning in 2WD mode. Thus the auto locking hubs must be stuck. Could this cause extra drag and thus overheating?
4).The oil light has been on for the last 3000 miles. As far as I can tell this is an electrical fault as I have been unable to get it to turn off by shorting out the connection on the oil pressure switch. The oil is circulating around the engine as I have a oil cooler that warms up shortly after the engine has started also the oil filter warms up after a few minutes running. Does the oil light also indicate oil levels in the difs and gearbox? If so this may be the cause....
Any ideas as to the cause of the overheating?