When it starts to run hot when idling, try running the garden hose through the radiator to see if it cools down... If it does cool down, then the issue is you are not getting enough air flow through the radiator... Then you need to get more air to flow through the radiator...
I agree with the comment on how the shroud looks like a wall that blocks the air and only allows it to flow through the two fan 'targets'...
