The problem with these engines running hot has a lot to do with both radiator hoses entering and departing on the same side of the radiator. When I rebuilt my 12ht I contacted Adrad Australia and they spelled out the problem for me with these engines only using half the radiator for cooling. The fix was to buy a new 4 core blank and have the top tank removed to run a cross over pipe inside the top tank. I had this done and have no overheating issues with my hj75 now but be warned this was not cheap and cost me around $800. If your truck has no air con you can simply turn your thermostat housing and run the later hzj79 style radiator that's 4 inches longer with the hoses entering top left and exerting bottom right.
