I had a similar problem with my 1997 3.9L +8, just over eight years ago. After some home work I decided to fit a Mulfab aluminium radiator also fitted 14” electric fan. Then as the cooling system was empty I decided to refill it with Evans waterless coolant. I do realise this was a bit of a controversial decision and some people will have different views on this.
But I have to say, it might have been over kill on my part, but it sorted the problem out and so far so good.
I hope you find this of help and manage to sort you overheating problem out.
Good luck
Regards
Steve
