[fireant911]

mca,
There are many possibilities that will work for this project; however, I do have first hand experience with the suggestion by emcon5 - Castrol SuperClean is great for this very task. What I did first was to remove the cooling fan so I had better access to the target area. I doused, via a spray bottle, the whole insides of the cooling shroud to removes years of gunk. It worked very well. I rigged up a wooden dowel / nylon brush combination to reach the recesses especially in the duct work leading to the oil cooler. I sprayed, allowed a soak time, and rinsed until all water coming from the cooler was clear. This process took a couple of hours as I was in no hurry and I wanted it to be thoroughly clean. After finishing from the top side I went underneath to give my best attempt at back-washing the cooler (garden hoze nozzle directly against the face of the cooler). Conceptually, this was to hopefully blow off any larger debris that may be in lying horizontally on the top surface to the cooler. You will get wet and dirty from this project. Wear eye protection because Castrol SuperClean does not belong in the eye. Do not do this in your driveway (out in the yard is better) - you may may want to temporarily use your oil changing container as a trap to catch the gunk. It is surprising how much 'stuff' I got out of mine.

I have been using Castrol SuperClean for years and have never seen any of the purported corrosion / discoloration as some have reported. Do not let it dry on the surface.