Power Wahser to Clean Rear Radiator

We have a 2001 Winnebago Journey DL with a 330HP Cat engine. When it was 2 or 3 years old the local Freightliner shop wanted to remove the radiator and clean the gunk from it at considerable cost to us. We called Freightliner in Gaffney and they told us to get the tube extended and then get underneath and spray every place on the radiator we could see with Simple Green and then turn the key a few times to bump the starter. This caused the fan to throw the Simple Green onto places where it had thrown the oil. Then we waited a couple of hours and then got underneath and sprayed with a garden hose. That cleaned it enough so that after dark when we shined a flashlight through the radiator from underneath, we could see the light from the back of the coach. We've only had one slight overheating problem since then, but it was 110 degrees out and we were going up a steep grade for a few miles with the dash A/C on (oops - should have thought to turn it off before the steep grade).