I've got a 2006 ford ranger thunder its the 2.5 litre tdci duratorq engine.
it has just recently started to overheat so naturally the coolant was checked and it was low so I drained it and added all new coolant drove it for 5 mins it overheated again.
then took the thermostat out and tested it in boiling water, It didn't work so got a new one and replaced it. drove it and it was fine for about 10 miles then overheated again
so removed the hoses and flushed the heater core all was fine there. did a full flush on the radiator and hoses to look for blocks, no blockages
removed the water pump to find that its fairly new and is working fine.
at a dead end with this does anyone have any suggestions or been in a similar situation themselves any help would be greatly appreciated as Only An apprentice so cannot afford an expensive bill at a shop so will be doing it myself

 

Welcome to the forum

Remove the heater hoses at the firewall and add coolant/water to radiator, the heater hoses allow any air trapped behind thermostat to get out of the engine
Once coolant is coming out of both hoses put them back on, air is OUT

We don't have your engine here in North America, we never had diesels after 1985/6, also our Rangers here were smaller than your T6 model
Australian Ranger forums are in english and they have your T6 Ranger there with diesels

If you are not seeing white smoke out the tail pipe then your head gasket should be OK

An engine that runs at normal temp on the highway but heats up at lower speeds or when stopped usually means the fan is not working as it should
Radiator needs air flow to do its job, at speed the vehicle provides that air flow, when going slow or stopped the fan does it