A filthy car needs washing but not just an ordinary car wash. It needs an intensive car wash using hydraulic hose to blast away the dirt and mud and other sticky substances. Ordinary washing with a sponge and a bucket of water does not do the trick anymore because of the smog.
I remember how my dad would just get a soapy water and an ordinary sponge to wash our car. Back then, the environmental factors on making a vehicle dirty was not as bad as now. Pollution has made it difficult to clean our cars.