Have been watching this forum which has given some great info so here's one I need help with- a little Hitachi ex40-2 that's heating after about 20 minutes work. Kubota engine, Radiator has been replaced with new one, new coolant, thermostat removed. Water pump is circulating fine it seems and new fan belt with proper tension. The engine is started and when warmed up can be put on full throttle without working the machine,and water temp gauge will eventually rise to just under halfway and stay there. The issue is when the machine is worked, tracking/digging using the dipper that after about 15-20 minutes the water temp gauge rises and will climb to just under the red line, I have never let it boil. If the bonnet is lifted while the machine is working it stays cooler for longer,if it is worked hard though even with bonnet open it will eventually heat. I have checked the under bonnet temperatures with infra red thermometer after it has been worked for approx 30 minutes and heat has risen,and the max temperatures I am getting are around 75 degrees celsius at the radiator cap and on the top of the oil cooler. I have checked the cooler and cleaned it, hydraulic filter in the tank has been replaced. New ISO 46 oil is being used. I notice also that when I stop working the hydraulics when water temperature is up,the water temp will eventually start dropping. So this is indicating to me an issue with hydraulics heating, causing the oil cooler to heat and in turn the water temperature heating. Any advice on what to do or where to go about remedying the issue? Thanks