I suspect your RRC VM diesel engine is very similar to the ones fitted to Jeep Cherokees from the early 1990's. Food for thought...

I've had a 3.5 in my Series 2 for over 20 years and have never had an overheating issue. I have a standard Series 3 radiator, with an 88°C thermostat and an electric fan from a Citroen BX diesel, mounted in front of the rad. My engine is fitted with the thermostat housing off a 3.9 Range Rover...