Hi, I have some problem with my 1997 XJ Sport 4.0 recently. The car is running normal when I constantly drive around 80km/h with a temperature needle remain in the middle of the indicator. But if I hit the gas and let it run a bit aggresive around 100-120km/h for 15-20 minutes the temperature will get up one more bar more than half of the indicator then the car start to loosing power. The car feels heavy/hard to run and with a ticking sound from the valves, it's feels like a manual gear vehicle climbing a hill and need to shift down (my car is automatic gear). If I keep the car running on that condition for about 15 minutes the coolant in reservoir tank will get boiled with a gurgling sound came from under the radiator cap as well.. Have check the radiator water, check the radiator cap, check the engine oil everythings was fine, no leakage and not less than standard. My car also equiped with extra fan and oil cooler as I'm staying in middle east.

Can anyone advised me what happened and how to solve it? Thanks