The underdrive pulleys are a regional thing: if you live up north, they work OK. If you live in one of the large metro areas in Florida, Texas, New Mexico or Arizona, you may have overheating problems. The heat bakes the pavement and everything gets really heat soaked. The 140* pavement can heat the air up to the point that the cooling system gets stressed and starts to get finicky. The higher the ambient temperature, the harder it is for the radiator to lose heat into the surrounding air.