How do blade cuffs help cool the engine?
Source: An Illustrated Dictionary of Aviation



The cuff is used to change the pitch of the blades (or to create an airfoil when there is none) near the spinner. The cuff increases the airflow near the engine cooling intakes. The cuff is large, and larger at the blade root because the linear speed in this area is very small compared to the tip.
Lockheed P3 Orion

 

Cuffed blades of a Lockheed P3 Orion. Top: Photo by palmerphoto at RedBubble. Bottom: Photo by MDLPhotoz at Flickr

North American P-51 Mustang, cuffed vs uncuffed


Awesome photo by Allan Grant/LIFE Magazine, via This Day in Aviation

Captioned:


  Joe De Bona and Jimmy Stewart with Thunderbird, their P-51C Mustang
  racer, April 1949. Placed on the ramp in front of the airplane is
  equipment that has been removed or replaced. Note the four “cuffed”
  Hamilton Standard propeller blades along the right side of the
  photograph. They have been replaced with un-cuffed and polished
  Hamilton Standard “paddle” blades.


More aviation photos by Allan Grant