I have experienced the following problem with my 1998 V70 Turbodiesel , automatic transmission with original Volvo oilcooler, installed according to their specifications.
While hauling a caravan at 80 km/hr in the mountains the dashtempindicator remained in the middle even while climbing steep hills. When the car had to pull extremely hard and long, the tempindicator went up, just reaching the red arrow.At that moment the engine would loose power en speed would drop to 45km/hr. (sitting duck)
This happened many times. After taking it slow for a while, the needle would drop again and the engine would regain power.
We found no failure messages at all, while checking the motormanagement
What causes this "overheating" ? radiators are clean on the outside and inside.
Is there a tempsensor telling the motormanagement to slow down the engine ?
Could a faulty Air Mass Meter cause this ?
Any information is appreciated.

Kind regards,
John