Outer Limits 4x4 Board

Hey guys yet another issue with my 98 2.8td gu patrol :-(
Went to go for a play the other day and I was heading out the highway sitting on 100km for about 7 minutes than all of a sudden the temp gauge went straight up.. I took it to the radiator shop go EVERYTHING chemically cleaned got a new top tank on the radiator and motor all pressure tested which showed no signs of cracked head or anything all up cost $470.
There is no oil in the water and not water in the oil and doesn't even go close to getting hot around town.. Its building pressure up somewhere because it blows coolant out the square hole in one of the bottle which apparently the whole is factory.. :-/ any ideas would be muchly appriecated

Make sure the cooling system is bled properly of all the air first. Trapped air will push the coolant out when it expands

Or its a possible blown head gasket. Overheated 2.8's can have head issues
Had a similar thing on my 4.2. No leaks, no water in oil, no bubbles in coolant at idle (possbily due to no boost pressure) just pushing the water out the reservoir bottle all the time and getting air in radiator. And the cooling system CO2 detectors dont work with diesels apparently...

Diesels dont make C02 like a petrol would hence why this wouldnt work. I would be looking into the head or possibly trying to bleed as stated above

also check your fan is working properly. bro in law had a 2.8 that would only heat up on the highway as well and his clutch fan was shagged. i would of thought it would heat up around town but it was fine and only got hot on the h/way.