I have found that even with a cold engine I can get a very clean engine and bay by spraying simple green everywhere under the hood, letting it soak for a few minutes and then hosing it off with water. From time to time I will aslo get under the car and spray the underside of the engine and all the trans that I can get to. Really helps to see if there are any more drips than normal (for my car!)

There have been no problems with dry rubber products and my driveway is cleaner for it. Plus it is cheap in bulk and better for the environment too.