4-6 minutes is a lot longer than you think, if you are speaking constantly and not "ummm'ing" a lot. If you want to break down the entire process into three steps - wash/prep, polish, and wax, then you will have time for an introduction (30-45) seconds, three main points of about 1 minute each, and a conclusion (30 seconds). Keep the talk structured and highlight the main points and importance of each step, and you should be able to cover everything.
In high school I was on the speech team and we would have to cover current events for 5-7 minutes with only a 30 minute prep time. 6 minutes is a lot longer than you think when you realize that you don't have enough material! Just outline your talk, practice a few times and add/remove where you need to and you will do great. I don't think that you will be able to deliver a very interesting, or long enough talk if you only talk about washing, or one area of the entire process.
You will probably get bonus points if you have a good attention grabber in your introduction (don't you wonder how cars on TV always look incredible!?) and can deliver the entire thing without having to read anything. That's why knowledge of the subject and a simple outline along with practice is crucial.