3126B engine overheating on 325CL Excavator

Dear all,

I have CAT 325 CL Excavator with 3126B engine .it has overheating problem when it works with bucket but when it works with jackhammer it's no problem.
Overheating start after working 30 minutes with bucket when we make the engine ideal the gage return back normal .
The engine has no oil consumption and also water consumption .
The action we take to solve the problem is
1.we changed termostat
2.we changed the cap
3.we changed the sensor
4.we washed the radiator core inside and outside
After we done all this there is no change finally we out the termostat and closing the bypass , it is working but after five hour the overheating start again .

So please I need help