Any
car wash liquid would be somewhat harsh if you use way too much. I use 3/4 capful per gallon for all my car washes which leaves enough suds for an average (AKA non-puterbum

) wash. A strong steam of water helps activate the foam.
IMO, Platinum products are awfully mild. I hear they're planning on putting some of their polymers in the wash (a la Z7) to help maintain the UPP shine.
~bw