Hitachi EX100-3 Overheating

Hi, I have a Hitachi EX100-3 excavator that is overheating after 30-40 min work in around 35 degrees celcius temperatures. It seems to be ok with light work on cooler days but pretty bad on these hotter days. After pulling the radiator out and having it cleaned I decided to check the water pump while the radiator was out. Upon pulling it out I noticed that someone (presumably one of the previous owners) has at some point over the years blanked off the bypass pipe that runs between the water...

Hitachi EX100-3 Overheating

Hitachi EX100-3 Overheating