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When you say "lower half", are you referring to painted surfaces? Like the areas that are prone to getting blasted with road tar? If that's the case, try Stoner's Tarminator. However, if you mean the undercarriage and wheel wells, there are a lot of heavy duty cleaners to use. I have a gallon of Meguiar's Super Degreaser on hand for that stuff.
Amazing Roll Off and P21S Total Auto Wash are both safe for paint, tires, wheel wells, engine bays, and several other surfaces. Supposedly, P21s TAW is the citrus degreaser that Paul Dalton uses.
Exactly "When you say "lower half", are you referring to painted surfaces? Like the areas that are prone to getting blasted with road tar? If that's the case, try Stoner's Tarminator. However, if you mean the undercarriage and wheel wells, there are a lot of heavy duty cleaners to use. I have a gallon of Meguiar's Super Degreaser on hand for that stuff. "
P21s Total Auto Wash would probably be the safest "degreaser" type product to use on paint. Remember that it or any other strong cleaner is going to remove any wax/sealant from the finish as well.
I normally start out with a heavy solution of car wash in a spray bottle. Saturate the affected areas, let dwell for a few minutes, and then proceed with the wash.