I found that the local car wash has an engine degreaser that can be sprayed on, let sit for a few minutes while I clean the tires/wheels, and then go back to the engine with soapy high pressure wash, it comes clean like new. Makes all the rubber look new, and I usually leave the engine running so that there is not the chance of an electrical misfire when I try to restart the engine. Give it a try, it is much easier than trying to use a brass wire brush or chemicals and cold water hose. Joe-JDC