I agree with the "look better" answer.

We always had to remove them from our 1948 70 Standard when threshing wheat.  The heat was too much and the engine ran cooler without them.  We also put pure water in the radiator for summer work, as the engine seemed to run cooler.  I know this is contrary to normal procedures, but it worked--less boiloff with pure water.  

 <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->