Just copied the following from website:-
G101 is professional strength multi-purpose cleaner that is unbeatable for intensive cleaning of neglected wheel arches, engine bays and undercarriage areas. However, the high strength of the solution must not be taken lightly, and care should always be taken to select the correct dilution strength for the task in hand, and to avoid letting it dry out fully before it is rinsed off, otherwise permanent stains may appear on treated surfaces.