Not what you think, and I didn't either. I didn't think my clutch fan was kicking in as much as it should so I decided to remove it and make sure it was clean. Sometimes the spring can get dirt and grease in it and not coil when its hot.

Well to my surprise the front of the radiator was caked with dirt and a bunch of other ****. Also just as I suspected the spring on the fan clutch was packed full of grease and dirt.

After a good cleaning with degreaser and my garden hose I am running 30 degrees cooler on the freeway.

Moral of the story is check the front of your radiator and fan clutch if you have one.