Well here's a little piece of info for you, on the label for Zep Citrus it says for shop use, use at full strength to degrease an engine. I decided to test this and guess what? It stripped the paint off the frame rails and parts of the hood. Did I use it correctly? Sure did, according to the label. I've always gone 4:1 with APC's but decided to test out the manufacturer's instructions. Have a problem believing this? Go to The Home Depot and look at the label for Zep Citrus. After receiving Optimum Power Clean I decided to run this test again on another vehicle. I used it 3:1 and straight and the paint remained on the metal. :xyxthumbs: