[sumdetailer]

Originally Posted by togwt

Undercarriage:
After removing dirt, road grime, and etc neutralise the effects of the acidic road salt on the suspension / undercarriage (See also Salt and Road salt)
Methodology
•Thoroughly spray an undiluted d-limoene based (citrus) cleaner (P2IS Total Auto Wash) and let it soak in; remove by thoroughly rinsing with water. If you have a pressure washer available, fill tank with d-limoene based (citrus) cleaner and spray undercarriage (do not use excess pressure as water may penetrate crevices and seams where it cannot drain, causing corrosion), let it soak and then remove with plain water
•Spray undercarriage with (POR-15 Marine Clean™) one application will leave no residues, noxious fumes or flammable solvents (Canada-POR15.com)
•Apply two coats (allowing first coat to dry) of a rust inhibitor paint (POR-15 Rust Inhibitor, allow drying between coats.
•Spray after a wash, and before detailing for best results, a low-gloss, dark finish that Adam’s Invisible Undercarriage Spray leaves behind - Car Wax, Car Polish, Auto Detail Supplies - Adam's Polishes

Whats the best way to get under there though? It would be tough to get a pressure washer gun underneath a car, unless you have some kind of large ram or lift in your garage.