You fail to notice that many here is asking WHY to do the wash with Dawn.
It probably won't hurt washing once with Dawn before a detail, but why do it? IMO it doesn't clean any better than a car wash soap. If you re-read this bit from Procter & Gamble:
"Your car surface and the dirt that gets on it are a lot different from the food soils and dishes that dishwashing liquids clean effectively". You will notice that P&G are saying that Dawn isn't designed for the kind of dirt that gets on cars, it is designed to remove food soils. Anyone struggling with food soils before a detail
Sure it will help to remove oils if you wanted to do that, but a APC dilluted correctly will work a lot better for this purpose. So again, why use Dawn? Also as DennisH posted, Dawn contains additives that replenish oils in the skin, and a kind of wax to help sheet water from dishes, why would you wan't to add those additives and conditioners to the surface of the car?
Sure it's cheap, but this being Autopia I wouldn't think the goal were to try and find the cheapest way to clean our cars...
